Porous Fluid Sensor

ABSTRACT

An optical element includes a porous layer with a network of a plurality of interconnected voids. The porous layer is optically diffusive to at least one wavelength of light when the network of interconnected voids is substantially free of fluid. The porous layer of the optical element undergoes a detectable optical change upon fluid ingress into the network or egress from the network of interconnected voids.

BACKGROUND

Detection of the wetness or dryness of a material can be useful in manyapplications. For example, detection of the presence or absence of afluid can indicate whether a packaged material is fresh or contaminated,the extent to which a fluid has traversed an arrangement of channels ina microfluidic device, or whether a disinfecting fluid remains presentin an enclosure to maintain an antimicrobial effect. However, fluiddetection can be time consuming or unreliable, and is difficult toperform without disturbing the material being evaluated. Techniques areneeded to create fluid sensors that rapidly and reproducibly assess thepresence of a fluid.

Some optical devices require selective control of light transmission ata point along an optical path, or through a surface of an opticalcomponent such as, for example, a lightguide. It can be difficult toaccurately control light transmission along the surface of an opticalcomponent at a reasonably low cost.

SUMMARY

In general, the present disclosure relates to a fluid sensor including alayer of a porous material with a network of interconnected voids. Fluidingress into or egress from the voids causes a change in the refractiveindex of the porous material, and the optical effect of this refractiveindex change can be utilized for fluid sensing. For example, the porousmaterial can be selected from materials with a very low refractive indexthat are optically diffusive when the voids are substantially free offluid (dry), and then become transmissive to at least one wavelength oflight when the voids contain a fluid (wet). In various embodiments, thischange in appearance as the porous material changes from a dry state toa wet state (or vice-versa) can provide a fluid sensor.

In one embodiment, the change in refractive index as the porous materialmoves between wet and dry states can provide a rapid visual indicationof the presence or absence of fluid in a closure member such as, forexample, a closure for a medical device, packaging, and the like.

In another embodiment, the change in refractive index as the porousmaterial moves between wet and dry states can be used to control lighttransmission at an interface between the porous polymeric film and anoptical component. In addition, the porous material can be placed at aselected position along an optical path, and the change in appearance ofthe porous material between wet and dry states can be used to controllight transmission along the optical path.

In one aspect, the present disclosure is directed to an optical elementthat includes a porous layer with a network of a plurality ofinterconnected voids. The porous layer is optically diffusive to atleast one wavelength of light when the network of interconnected voidsis substantially free of fluid. The porous layer of the optical elementundergoes a detectable optical change upon fluid ingress into thenetwork or egress from the network of interconnected voids.

In another aspect, the present disclosure is directed to an opticalelement including a porous polymeric film with a network of a pluralityof interconnected voids. The porous polymeric film is opticallydiffusive to at least one wavelength of light when the network ofinterconnected voids is substantially free of fluid, and wherein theporous polymeric film undergoes a detectable optical change upon fluidingress into the network, or fluid egress from the network, ofinterconnected voids. A first polymeric film is on a first major surfaceof the porous polymeric film; and a second polymeric film different fromthe first polymeric film, on a second major surface of the porouspolymeric film; wherein the first polymeric film is transmissive tovisible light and the second polymeric film includes comprises at leastone of a pigment, a dye, an indicia, and combinations thereof.

In another aspect, the present disclosure is directed to an opticalelement including a porous polymeric film with a network of a pluralityof interconnected voids, wherein the porous polymeric film is opticallydiffusive to at least one wavelength of light when the network ofinterconnected voids is substantially free of fluid, and wherein theporous polymeric film undergoes a detectable optical change upon fluidingress into the network or egress from the network of interconnectedvoids. A first interference reflector on a first major surface of theporous polymeric film; and a second interference reflector, which may bethe same or different from the first interference reflector, on thesecond major surface of the porous polymeric film.

In another aspect, the present disclosure is directed to a closuremember. The closure member includes a body with a fluid sensor disposedon at least a portion thereof, wherein the fluid sensor comprises alayer of a porous material with a network of interconnected voids,wherein the layer of the porous material is optically diffusive to atleast one wavelength of light when the network of interconnected voidsis substantially free of fluid, and wherein the layer of the porousmaterial undergoes a detectable optical change and becomes transmissiveto the at least one wavelength of light upon fluid ingress into thenetwork or egress from the network of interconnected voids.

In another aspect, the present disclosure is directed to anantimicrobial closure member with a body that is transmissive to atleast one wavelength of light over at least a portion thereof. The bodyincludes an interior chamber, and an antimicrobial fluid in the body. Afluid sensor is in the interior chamber, wherein the fluid sensorincludes a layer of a porous material. At least one evaporative pathwayis between the interior chamber and an exterior of the body. The layerof the porous material is optically diffusive to at least one wavelengthof light when the network is substantially free of an antimicrobialliquid, and wherein the fluid sensor undergoes a detectable opticalchange and becomes transmissive to the at least one wavelength of lightupon ingress or egress of an antimicrobial liquid from the fluid sensor.

In another aspect, the present disclosure is directed to anantimicrobial closure member: a body that is transmissive to at leastone wavelength of light over at least a portion thereof, wherein thebody includes an interior chamber; a fluid sensor in the interiorchamber, wherein the fluid sensor includes a porous polymeric film, andwherein at least a portion of the porous polymeric film is filled withan antimicrobial fluid; wherein the porous polymeric film is opticallydiffusive to at least one wavelength of light when the network issubstantially free of the antimicrobial liquid, and wherein the fluidsensor undergoes a detectable optical change and becomes transmissive tothe at least one wavelength of light upon egress of the antimicrobialliquid from the fluid sensor.

In another aspect, the present disclosure is directed to a closuredevice including a body with an interior chamber; a fluid in theinterior chamber; a component in the interior chamber of the body,wherein the component includes a fluid sensor with a layer of a porousmaterial; wherein the fluid sensor undergoes a detectable optical changebased on the presence of fluid in the interior chamber of the closuredevice.

In another aspect, the present disclosure is directed to an opticaldevice, including: a lightguide with a first major surface; and anoptical switch including a layer of a porous material with a first majorsurface and a second major surface, wherein the second major surface ofthe layer of the porous material is on the first major surface of thelightguide, and wherein the porous material has a network ofinterconnected voids; and wherein the layer of the porous material isoptically diffusive to at least one wavelength of light when the networkof voids is substantially free of a fluid, and wherein the opticalswitch undergoes a detectable optical change to become opticallytransmissive to the at least one wavelength of light upon ingress oregress of the fluid from the network of voids.

In another aspect, the present disclosure is directed to an opticaldevice including a lightguide with a first major surface and a secondmajor surface; a light scattering layer on the first major surface ofthe lightguide; and an optical switch on the second major surface of thelightguide, wherein the optical switch includes a porous polymeric filmwith a first major surface and a second major surface, wherein the firstmajor surface of the porous polymeric film is on the second majorsurface of the lightguide, wherein the porous polymeric film has anetwork of interconnected voids; and wherein the porous polymeric filmis optically diffusive to at least one wavelength of light when thenetwork is substantially free of a fluid, and wherein the optical switchundergoes a detectable optical change upon ingress or egress of thefluid from the network; and a light absorbing layer on the second majorsurface of the porous polymeric film.

In another aspect, the present disclosure is directed to an opticaldevice including a cylindrical lightguide with a first major surface anda second major surface; and an optical switch including: a layer of aporous material with a first major surface and a second major surface,wherein the first major surface of the layer of the porous material ison an exterior surface the lightguide, wherein the layer of the porousmaterial has a network of interconnected voids; and wherein the layer ofthe porous material is optically diffusive to at least one wavelength oflight when the network of voids is substantially free of a fluid, andwherein the optical switch undergoes a detectable optical change tobecome optically transmissive to the at least one wavelength of lightupon ingress or egress of the fluid from the network of voids; and alight absorbing layer on the second major surface of the layer of theporous material.

In another aspect, the present disclosure is directed to an opticaldevice including a light transmissive component with an optical path;and a layer of a porous material in the optical path, wherein the layerof the porous material has a network of interconnected voids; andwherein the layer of the porous material is optically diffusive to atleast one wavelength of light when the network of voids is substantiallyfree of a fluid, and wherein the optical switch undergoes a detectableoptical change to become optically transmissive to the at least onewavelength of light upon ingress or egress of the fluid from the networkof voids.

In another aspect, the present disclosure is directed to an opticaldevice including a retroreflector; and a layer of a porous material onat least a portion of a major surface of the retroreflector, wherein thelayer of the porous material has a network of interconnected voids; andwherein the layer of the porous material is optically diffusive to atleast one wavelength of light when the network of voids is substantiallyfree of a fluid, and wherein the optical switch undergoes a detectableoptical change to become optically transmissive to the at least onewavelength of light upon ingress or egress of the fluid from the networkof voids.

In another aspect, the present disclosure is directed to an opticalelement, including: a porous polymeric film having a first portion witha network of a plurality of interconnected voids, wherein the firstportion of the porous polymeric film is optically diffusive to at leastone wavelength of light when the network of interconnected voids issubstantially free of fluid, and wherein the first portion of the porouspolymeric film undergoes a detectable optical change upon fluid ingressinto the network, or fluid egress from the network, of interconnectedvoids; a filler in a second portion of the porous polymeric film; afirst polymeric film on a first major surface of the porous polymericfilm; and a second polymeric film different from the first polymericfilm, on a second major surface of the porous polymeric film; whereinthe first polymeric film is transmissive to visible light and the secondpolymeric film comprises at least one of a pigment, a dye, an indicia,and combinations thereof.

In another aspect, the present disclosure is directed to a microfluidicdevice, including: a substrate with a network of microchannelsconfigured to transport a fluid; and a fluid sensor in fluidcommunication with the network of microchannels, wherein the fluidsensor has a porous polymeric film with a network of a plurality ofinterconnected voids, wherein the porous polymeric film is opticallydiffusive to at least one wavelength of light when the network issubstantially free of fluid, and wherein the fluid sensor undergoes adetectable optical change upon fluid ingress into the network or egressfrom the network to become optically transmissive at the at least onewavelength to provide a visual indication of movement of a fluid throughthe network of channels in the substrate.

In another aspect, the present disclosure is directed to a method,including: selecting a porous polymeric film with a network of pluralityof interconnected voids, wherein the porous polymeric film has a firstrefractive index when the network is substantially free of a fluid, anda second refractive index, different from the first refractive index,when the network includes a predetermined amount of a fluid; introducinga fluid into the network; and detecting an optical change in the porouspolymeric film to determine fluid ingress into the network or egressfrom the network.

In another aspect, the present disclosure is directed to a method,including: applying on a light transmissive surface of an optical devicea light switch having a porous polymeric film with a network ofplurality of interconnected voids, wherein the porous polymeric film hasa first refractive index when the network is substantially free of afluid, and a second refractive index, different from the firstrefractive index, when the network comprises a predetermined amount of afluid; introducing a fluid into the network; and detecting an opticalchange in the porous polymeric film to control light transmission acrossthe light transmissive surface.

In another aspect, the present disclosure is directed to an opticalelement, including: a porous polymeric film having a first portion witha network of a plurality of interconnected voids, wherein the firstportion of the porous polymeric film is optically diffusive to at leastone wavelength of light when the network of interconnected voids issubstantially free of fluid, and wherein the first portion of the porouspolymeric film undergoes a detectable optical change upon fluid ingressinto the network, or fluid egress from the network, of interconnectedvoids; a filler in a second portion of the porous polymeric film; afirst polymeric film is on a first major surface of the porous polymericfilm; and a second polymeric film different from the first polymericfilm, on a second major surface of the porous polymeric film; whereinthe first polymeric film is transmissive to visible light and the secondpolymeric film includes at least one of a pigment, a dye, an indicia,and combinations thereof.

The details of one or more examples of this disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of this disclosure will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic cross-sectional view of an embodiment of a porousmaterial in the absence of a fluid.

FIG. 1B is a schematic cross-sectional view of an embodiment of a porousmaterial including a fluid therein.

FIG. 2A is a schematic cross-sectional view of an embodiment of a layerof a porous material.

FIGS. 2B-2G are schematic cross-sectional views of gradient layers ofporous materials.

FIG. 3 is a schematic cross-sectional view of an embodiment of anoptical construction.

FIG. 4 is a schematic cross-sectional view of an embodiment of anoptical construction.

FIG. 5 is a schematic cross-sectional view of an optical stack includinga layer of a porous material.

FIGS. 6A-C are schematic cross-sectional views of various embodiments ofclosure members including a fluid sensor with a layer of a porousmaterial.

FIG. 6D is a schematic cross-sectional view of an embodiment of aclosure member including a plunger with a fluid sensor with a layer of aporous material.

FIG. 6E is a schematic cross-sectional view of an embodiment of aclosure member including a liquid reservoir and a fluid sensor with alayer of a porous material.

FIG. 7 is a schematic cross-sectional view of an embodiment of a fluidsensor.

FIGS. 8A-8B are schematic cross-sectional views of an embodiment of alight guide configuration.

FIGS. 9A and 9B are schematic cross-sectional views of an embodiment ofa light guide configuration.

FIG. 10A is a schematic cross-sectional view of an embodiment of a lightguide indicator system.

FIG. 10B is a schematic overhead view of a cross section of the lightguide indicator of FIG. 10A.

FIGS. 11A-11B are schematic overhead view of a cross section of thelight guide indicator of FIG. 10A.

FIG. 12A is a schematic, cross-sectional view of an embodiment of anoptical component including a layer of a porous material.

FIG. 12B is a schematic, cross-sectional view of an embodiment of anoptical component including a layer of a porous material.

FIG. 13A is a schematic transverse cross-sectional view of an embodimentof a microfluidic device.

FIG. 13B is a schematic overhead view of the microfluidic device of FIG.12A.

FIGS. 14A-14F are photographs of fluid deposited on the surface of afluid sensor including a porous polymeric film of Example 1.

FIGS. 15A-15D are photographs of a fluid deposited on a fluid sensorincluding a seal layer overlying a porous polymeric film according toExample 2.

FIG. 16 is a photograph of a cross section of a porous polymeric film.

Like symbols in the drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1A is a schematic cross-sectional view of an optical construction100A that includes a layer 102 of a porous material including aplurality of voids (not shown in FIG. 1A). When the porous layer 102 isdry, the layer 102 is mostly air, and is highly reflective to incominglight rays 103. The layer 102 has a substantially opaque appearance, dueat least in part to refractive index differences at the plurality ofscattering sites at the air-material interfaces within the layer 102. Asshown schematically in FIG. 1B, in an optical construction 100B, atleast a portion of the porous layer 104 is filled with a fluid, and thepresence of the fluid in the voids reduces the number of scatteringsites encountered by incoming light rays 105, which substantiallyeliminates the refractive indices at the air/material interfaces withinthe layer, and causes the layer 104 to be substantially transmissive toat least one wavelength of light.

When the fluid is removed from the voids in the porous layer 104 suchas, for example, by evaporation, drying, chemical reaction, or the like,the layer 104 reverts to the opaque appearance of the layer 102 of FIG.1A. Since the porous layers 102, 104 can be reversibly converted betweenopaque and transmissive states, the porous layers 102, 104 of FIGS.1A-1B thus can be utilized to provide an optical sensor configured todetect the presence or absence of the fluid in the voids thereof.

A wide variety of porous materials may be used for the porous layers102, 104. Suitable examples include, but are not limited to, the porousmaterials disclosed in U.S. Pat. Nos. 8,964,146 and 9,279,918; and in WO2010/120468.

In general, suitable porous materials exhibit low-index-like opticalproperties, and in some embodiments can exhibit low-index-like opticalproperties. In some embodiments, the porosity can vary along a thicknessdirection, which forms a gradient porous material. Some of the gradientporous materials exhibit a local porosity, which may be described by alocal void volume fraction, or as a local void size distribution, thatvaries along a thickness direction thereof.

Some suitable porous materials, when substantially free of fluid, have alow optical haze and a low effective index of refraction, such as anoptical haze of less than about 5%, and an effective index of refractionthat is less than about 1.35. Some suitable porous materials, whensubstantially free of fluid, have a high optical haze, such as anoptical haze of greater than about 50%, and/or high diffuse opticalreflectance, while manifesting some low-index-like optical properties,such as, for example, the ability to support total internal reflectionor enhance internal reflection.

The porous materials include a plurality of interconnected voids, or anetwork of voids, dispersed in a polymeric binder or matrix material. Atleast some of the voids in the plurality or network are connected to oneanother via hollow tunnels or hollow tunnel-like passages.

In some embodiments, a void or multiple voids may include one or moresmall fiber- or string-like objects that include, for example, a binderand/or nanoparticles. In some cases, a void may include particles orparticle agglomerates that may be attached to the binder, or may beloose within the void. Some suitable porous materials include multiplepluralities of interconnected voids or multiple networks of voids wherethe voids in each plurality or network are interconnected. In somecases, in addition to multiple pluralities of interconnected voids, theporous materials include a plurality of closed or unconnected voids,which means that the voids are not connected to other voids via tunnels.

In some embodiments, the porous materials can include a plurality ofinterconnected voids or a network of voids having a local volumefraction that varies along a thickness direction of the material. Asused herein, “local volume fraction” means the volume fraction of acomponent (e.g., the plurality of interconnected voids) measured on alocal scale, for example, in a region less than about 10%, or less thanabout 5%, or less than about 3%, or less than about 1% of the totalthickness of a layer of the material. The local volume fraction ofinterconnected voids can vary across the thickness of the layer of theporous material, such that the local volume fraction of interconnectedvoids proximate one surface of the layer can be greater or less than thelocal volume fraction of interconnected voids proximate an opposingsurface of the layer. The bulk volume fraction of interconnected voidsis the ratio of the volume of voids in the layer of the porous materialto the total volume of the layer.

In some cases, the local volume fraction of interconnected voids can beclose to zero proximate one surface of the porous material (that is,there are very few interconnected voids), and the layer can be said tobe essentially “sealed” on that surface. In some cases, the local volumefraction of interconnected voids can vary in a continuous mannerthroughout the porous material, such as either a monotonic increase ordecrease in the local volume fraction across the thickness directionthereof. In some cases, the local volume fraction of interconnectedvoids can go through a local maximum or a local minimum in the volumefraction of interconnected voids across the thickness direction of thelayer of the porous material. In some cases, the local volume fractionof interconnected voids can vary in a discontinuous manner along thethickness direction of the porous material, for example, a step-changein the local volume fraction of interconnected voids.

Control of the local volume fraction of interconnected voids can beuseful in several applications including, for example, when a materialis coated on a surface of a layer of the porous material. In some cases,the coated porous material may include a solvent or other high mobilitycomponent such as, for example, a low molecular weight curable material,which can penetrate the interconnected voids of the porous materials. Insome cases, the coated porous material may include a thermoplastic solidor a gelled material, such as a transfer adhesive or a pressuresensitive adhesive (PSA) that, upon thermal cycling or aging, canpenetrate into the porous structure of interconnected voids. Penetrationof a material into the interconnected voids of the porous material canalter properties of the layer, including, for example, increasing therefractive index in the penetration region.

In one particular embodiment, a change in the local volume fraction ofthe interconnected voids can provide control over this penetrationproximate one surface of a layer of the porous material, whilemaintaining a desired local volume fraction of the interconnected voidsproximate an opposing surface of the layer. In some cases, the localvolume fraction of interconnected voids proximate one surface of theporous material can be lower than the bulk volume fraction ofinterconnected voids and also lower than the local volume fractionproximate the opposing surface of the layer. In some cases, the localvolume fraction of interconnected voids can be decreased so that onlylimited infusion can take place. In some cases, a lower volume fractionof interconnected voids in a porous polymeric material can improve thestructural integrity and durability of the layer.

In some embodiments, the local volume fraction of interconnected voidscan be decreased to near zero local volume fraction of interconnectedvoids, effectively sealing the surface of the porous material. Controlof the local volume fraction of interconnected voids can includetechniques such as, for example, inhibiting or promoting the rate andextent of cure on one or more surface of the porous material, infusionof a material to at least partially fill a portion of the voids, and thelike. In general, control over the local volume fraction ofinterconnected voids can be accomplished by techniques described in, forexample, WO 2011/050232, entitled “PROCESS FOR GRADIENT NANOVOIDEDARTICLE.”

Some porous materials support total internal reflection (TIR) orenhanced internal reflection (EIR) by virtue of including a plurality ofvoids. When light that travels in an optically clear non-porous mediumis incident on a stratum possessing high porosity, the reflectivity ofthe incident light is much higher at oblique angles than at normalincidence. In the case of no or low haze voided films, the reflectivityat oblique angles greater than the critical angle is close to about100%. In such cases, the incident light undergoes total internalreflection (TIR). In the case of high haze voided porous materials, theoblique angle reflectivity can be close to 100% over a similar range ofincident angles even though the light may not undergo TIR. This enhancedreflectivity for high haze films is similar to TIR and is designated asEnhanced Internal Reflectivity (EIR). As used herein, by a porous orvoided material enhancing internal reflection (EIR), it is meant thatthe reflectance at the boundary of the voided and non-voided strata ofthe layer is greater with the voids than without the voids.

In some embodiments, the voids in the porous materials have an index ofrefraction n_(v) and a permittivity ∈_(v), where n_(v) ²=∈_(v), and thebinder has an index of refraction n_(b) and a permittivity ∈_(b), wheren_(b) ²=∈_(b). In general, the interaction of a porous material withlight, such as light that is incident on, or propagates in, a layer ofthe material, depends on a number of film characteristics such as, forexample, the layer thickness, the binder index, the void or void index,the void shape and size, the spatial distribution of the voids, and thewavelength of light. In some cases, light that is incident on orpropagates within the gradient porous material, “sees” or “experiences”an effective permittivity ∈_(eff) and an effective index n_(eff), wheren_(eff) can be expressed in terms of the void index n_(v), the binderindex n_(b), and the void porosity or volume fraction “f.” In suchcases, the porous materials are sufficiently thick, and the voids aresufficiently small, so that light cannot resolve the shape and featuresof a single or isolated void. In such cases, the size of at least amajority of the voids, such as at least 60% or 70% or 80% or 90% of thevoids, is not greater than about λ/5, or not greater than about λ/6, ornot greater than about λ/8, or not greater than about λ/10, or notgreater than about λ/20, where is the wavelength of light.

In some cases, light that is incident on a porous material is a visiblelight meaning that the wavelength of the light is in the visible rangeof the electromagnetic spectrum. In such cases, the visible light has awavelength that is in a range from about 380 nm to about 750 nm, or fromabout 400 nm to about 700 nm, or from about 420 nm to about 680 nm. Insuch cases, the porous material has an effective index of refraction andincludes a plurality of voids if the size of at least a majority of thevoids, such as at least 60% or 70% or 80% or 90% of the voids, is notgreater than about 70 nm, or not greater than about 60 nm, or notgreater than about 50 nm, or not greater than about 40 nm, or notgreater than about 30 nm, or not greater than about 20 nm, or notgreater than about 10 nm.

In some embodiments, the porous materials are sufficiently thick so thata layer of the material can reasonably have an effective index that canbe expressed in terms of the indices of refraction of the voids and thebinder, and the void or void volume fraction or porosity. In such cases,the thickness of the layer of the porous material is not less than about100 nm, or not less than about 200 nm, or not less than about 500 nm, ornot less than about 700 nm, or not less than about 1,000 nm.

When the voids in the porous material are sufficiently small and theoptical film is sufficiently thick, a layer of the material has aneffective permittivity ∈_(eff) that can be expressed as:

∈_(eff) =f∈ _(v)+(1−f)∈_(b)  (1)

The effective index n_(eff) of the porous layer can be expressed as:

n _(eff) ² =fn _(v) ²+(1−f)n _(b) ²  (2)

In some cases, such as when the difference between the indices ofrefraction of the voids and the binder is sufficiently small, theeffective index of the layer of the porous material can be approximatedby the following expression:

n _(eff) =fn _(v)+(1−f)n _(b)  (3)

The effective refractive index of the layer of the porous material isthe volume weighted average of the indices of refraction of the voidsand the binder. For example, a porous material that has a void volumefraction of about 50% and a binder that has an index of refraction ofabout 1.5, has an effective index of about 1.25.

A layer of one such porous material 300A is illustrated in FIG. 2, whichincludes a network of voids or plurality of interconnected voids 320 anda plurality of optional particles 340 dispersed substantially uniformlywithin a binder 310. The layer of the porous material 300A has a porousinterior by virtue of the presence of network of voids 320 within thelayer. In general, the porous material can include one or more networksof interconnected voids. For example, the network of voids 320 can beregarded to include interconnected voids or voids 320A-320C.

In some embodiments, a local volume fraction of interconnected voids,for example a first local volume fraction of interconnected voids 370Aand a second volume fraction of interconnected voids 375A, can varyalong a thickness t₁ direction within the layer 300A. The local volumefraction of interconnected voids, and void size distribution, can varyalong the thickness direction. In some cases, the network of voids 320forms one or more passages between first and second major surfaces 330and 332, respectively.

The network of voids can be regarded to include a plurality ofinterconnected voids. Some of the voids can be at a surface of the layerof the porous material 300A and can be regarded to be surface voids. Forexample, in the exemplary layer of the porous material 300A, voids 320Dand 320E are at a second major surface 332 of the film and can beregarded as surface voids 320D and 320E, and voids 320F and 320G are ata first major surface 330 of the layer and can be regarded as surfacevoids 320F and 320G. Some of the voids, such as for example voids 320Band 320C, are within the interior of the layer 300A and away from theexterior surfaces thereof, and can be regarded as interior voids 320Band 320C, even though an interior void can be connected to a majorsurface via, for example, other voids.

The voids 320 have a size d₁ that can generally be controlled bychoosing suitable composition and fabrication techniques, such ascoating, drying and curing conditions. In general, d₁ can be any desiredvalue in any desired range of values. For example, in some cases, atleast a majority of the voids, such as at least 60% or 70% or 80% or 90%or 95% of the voids, have a size that is in a desired range. Forexample, in some cases, at least a majority of the voids, such as atleast 60% or 70% or 80% or 90% or 95% of the voids, have a size that isnot greater than about 10 microns, or not greater than about 7 microns,or not greater than about 5 microns, or not greater than about 4microns, or not greater than about 3 microns, or not greater than about2 microns, or not greater than about 1 micron, or not greater than about0.7 microns, or not greater than about 0.5 microns.

In some cases, the plurality of interconnected voids 320 has an averagevoid or void size that is not greater than about 5 microns, or notgreater than about 4 microns, or not greater than about 3 microns, ornot greater than about 2 microns, or not greater than about 1 micron, ornot greater than about 0.7 microns, or not greater than about 0.5microns.

In some embodiments, some of the voids can be sufficiently small so thattheir primary optical effect is to reduce the effective index, whilesome other voids can reduce the effective index and scatter light, whilestill some other voids can be sufficiently large so that their primaryoptical effect is to scatter light.

The optional particles 340 have a size d₂ that can be any desired valuein any desired range of values. For example, in some cases at least amajority of the particles, such as at least 60% or 70% or 80% or 90% or95% of the particles, have a size that is in a desired range. Forexample, in some cases, at least a majority of the particles, such as atleast 60% or 70% or 80% or 90% or 95% of the particles, have a size thatis not greater than about 5 microns, or not greater than about 3microns, or not greater than about 2 microns, or not greater than about1 micron, or not greater than about 700 nm, or not greater than about500 nm, or not greater than about 200 nm, or not greater than about 100nm, or not greater than about 50 nm.

In some cases, plurality of particles 340 has an average particle sizethat is not greater than about 5 microns, or not greater than about 3microns, or not greater than about 2 microns, or not greater than about1 micron, or not greater than about 700 nm, or not greater than about500 nm, or not greater than about 200 nm, or not greater than about 100nm, or not greater than about 50 nm.

In some cases, some of the particles can be sufficiently small so thatthey primary affect the effective index, while some other particles canaffect the effective index and scatter light, while still some otherparticles can be sufficiently large so that their primary optical effectis to scatter light.

In some cases, d₁ and/or d₂ are sufficiently small so that the primaryoptical effect of the voids and the particles is to affect the effectiveindex of layer of the porous material 300A. For example, in such cases,d₁ and/or d₂ are not greater than about λ/5, or not greater than aboutλ/6, or not greater than about λ/8, or not greater than about λ/10, ornot greater than about λ/20, where is the wavelength of light. Asanother example, in such cases, d₁ and d₂ are not greater than about 70nm, or not greater than about 60 nm, or not greater than about 50 nm, ornot greater than about 40 nm, or not greater than about 30 nm, or notgreater than about 20 nm, or not greater than about 10 nm. In suchcases, the voids and the particles may also scatter light, but theprimary optical effect of the voids and the particles is to define aneffective medium in the layer 300A that has an effective index. Theeffective index depends, in part, on the indices of refraction of thevoids, the binder, and the particles. In some cases, the effective indexis a reduced effective index, meaning that the effective index is lessthan the index of the binder and the index of the particles.

In cases where the primary optical effect of the voids and/or theparticles is to affect the index, d₁ and d₂ are sufficiently small sothat a substantial fraction, such as at least about 60%, or at leastabout 70%, or at least about 80%, or at least about 90%, or at leastabout 95% of voids 320 and particles 340 have the primary optical effectof reducing the effective index. In such cases, a substantial fraction,such as at least about 60%, or at least about 70%, or at least about80%, or at least about 90%, or at least about 95% the voids and/or theparticles, have a size that is in a range from about 1 nm to about 200nm, or from about 1 nm to about 150 nm, or from about 1 nm to about 100nm, or from about 1 nm to about 50 nm, or from about 1 nm to about 20nm.

In some cases, the index of refraction n₁ of particles 340 can besufficiently close to the index n_(b) of binder 310, so that theeffective index does not depend, or depends very little, on the index ofrefraction of the particles. In such cases, the difference between n₁and n_(b) is not greater than about 0.01, or not greater than about0.007, or not greater than about 0.005, or not greater than about 0.003,or not greater than about 0.002, or not greater than about 0.001. Insome cases, particles 340 are sufficiently small and their index issufficiently close to the index of the binder, that the particles do notprimarily scatter light or affect the refractive index. In such cases,the primary effect of the particles can, for example, be to enhance thestrength of the layer of the porous material 300A. In some cases,particles 340 can enhance the process of making the porous material,although in some embodiments the layer 300A can be made with noparticles.

In cases where the primary optical effect of network of voids 320 andparticles 340 is to affect the effective index and not to, for example,scatter light, the optical haze of the layer of porous material 300Athat is due to voids 320 and particles 340 is not greater than about 5%,or not greater than about 4%, or not greater than about 3.5%, or notgreater than about 4%, or not greater than about 3%, or not greater thanabout 2.5%, or not greater than about 2%, or not greater than about1.5%, or not greater than about 1%. In such cases, the effective indexof the effective medium of the layer of porous material is not greaterthan about 1.35, or not greater than about 1.3, or not greater thanabout 1.25, or not greater than about 1.2, or not greater than about1.15, or not greater than about 1.1, or not greater than about 1.05.

In cases where the layer of porous material 300A can reasonably have areduced effective index, the thickness of the layer is not less thanabout 100 nm, or not less than about 200 nm, or not less than about 500nm, or not less than about 700 nm, or not less than about 1,000 nm, ornot less than about 1500 nm, or not less than about 2000 nm.

In some cases, d₁ and/or d₂ are sufficiently large so that their primaryoptical effect is to scatter light and produce optical haze. In suchcases, d₁ and/or d₂ are not less than about 200 nm, or not less thanabout 300 nm, or not less than about 400 nm, or not less than about 500nm, or not less than about 600 nm, or not less than about 700 nm, or notless than about 800 nm, or not less than about 900 nm, or not less thanabout 1000 nm. In such cases, the voids and the particles may alsoaffect the index, but their primarily optical effect is to scatterlight. In such cases, light incident on the layer 300A can be scatteredby both the voids and the particles.

In some cases, layer of porous material 300A has a low optical haze. Insuch cases, the optical haze of the layer 300A is not greater than about5%, not greater than about 4%, not greater than about 3.5%, not greaterthan about 4%, not greater than about 3%, not greater than about 2.5%,not greater than about 2%, not greater than about 1.5%, or not greaterthan about 1%. In such cases, the layer of porous material 300A can havea reduced effective index that is not greater than about 1.35, notgreater than about 1.3, not greater than about 1.2, not greater thanabout 1.15, not greater than about 1.1, or not greater than about 1.05.For light normally incident on the layer of the porous material 300A,optical haze, as used herein, is defined as the ratio of the transmittedlight that deviates from the normal direction by more than 4 degrees tothe total transmitted light. Haze values were measured using a HAZE-GARDPLUS haze meter (available from BYK-Gardner, Silver Springs, Md.)according to the procedure described in ASTM D1003.

In some cases, the layer of the porous material 300A has a high opticalhaze. In such cases, the haze of the porous material 300A is not lessthan about 40%, not less than about 50%, not less than about 60%, notless than about 70%, not less than about 80%, not less than about 90%,or not less than about 95%. In some cases, the layer 300A can have anintermediate optical haze, for example, between about 5% and about 50%optical haze.

In some embodiments, the layer of the porous material 300A has a highdiffuse optical reflectance. In such cases, the diffuse opticalreflectance of the layer 300A is not less than about 30%, not less thanabout 40%, not less than about 50%, or not less than about 60%.

In some embodiments, the layer of the porous material 300A has a highoptical clarity. For light normally incident on the layer 300A, opticalclarity, as used herein, refers to the ratio (T₂-T₁)/(T₁+T₂), where T₁is the transmitted light that deviates from the normal direction between1.6 and 2 degrees, and T₂ is the transmitted light that lies betweenzero and 0.7 degrees from the normal direction. Clarity values weremeasured using a Haze-Gard Plus haze meter from BYK-Gardner. In thecases where the layer of the porous material 300A has a high opticalclarity, the clarity is not less than about 40%, or not less than about50%, or not less than about 60%, or not less than about 70%, or not lessthan about 80%, or not less than about 90%, or not less than about 95%.

In some embodiments, the layer of the porous material 300A has a lowoptical clarity. In such cases, the optical clarity of the layer 300A isnot greater than about 10%, not greater than about 7%, not greater thanabout 5%, not greater than about 4%, not greater than about 3%, notgreater than about 2%, or not greater than about 1%.

In general, the layer of the porous material 300A can have any porosityor void volume fraction that may be desirable in an application. In somecases, the volume fraction of plurality of voids 320 in the layer 300Ais not less than about 20%, not less than about 30%, not less than about40%, not less than about 50%, not less than about 60%, not less thanabout 70%, not less than about 80%, or not less than about 90%.

In some cases, the layer of the porous material 300A can manifest somelow-index properties, even if the film has a high optical haze and/ordiffuse reflectance. For example, in such cases, the layer 300A cansupport TIR at angles that correspond to an index that is smaller thanthe index n_(b) of the binder 310.

In some embodiments, the particles 340, such as particles 340A and 340B,are solid particles. In some cases, layer of the porous material 300Amay additionally or alternatively include a plurality of hollow orporous particles 350.

The particles 340 can be any type of particles that may be desirable inan application, and may selected from organic or inorganic particles.For example, in some non-limiting embodiments, the particles 340 can besilica, zirconium oxide or alumina particles.

The particles 340 can have any shape that may be desirable or availablein an application, and can have a regular or an irregular shape. Invarious embodiments, the particles 340 can be approximately spherical,or can be elongated. In such cases, the layer of the porous material300A includes a plurality of elongated particles 340B. In some cases,elongated particles 340B have an average aspect ratio that is not lessthan about 1.5, or not less than about 2, or not less than about 2.5, ornot less than about 3, or not less than about 3.5, or not less thanabout 4, or not less than about 4.5, or not less than about 5. In somecases, the particles 340 can be in the form or shape of astring-of-pearls (such as those available from Nissan Chemical, Houston,Tex., under the trade designation SNOWTEX-PS), or aggregated chains ofspherical or amorphous particles, such as fumed silica. In someembodiments, the particles 340 can be highly structured, high surfacearea fumed metal oxides, such as fumed silica oxides, can be used in amixture of a suitable binder to form a composite structure that combinesbinder, particles, voids, and optionally crosslinkers or other adjuvantmaterials. The desirable binder to particle ratio depends on the type ofprocess used to form the interconnected voided structure. Suitablematerials and processes include, but are not limited to, those describedin U.S. Pat. No. 9,588,262, which is incorporated herein by reference.

The particles 340 may or may not be functionalized. In some cases, theparticles 340 are functionalized so that particles 340 can be dispersedin a desired solvent or binder 310 with no, or very little, clumping. Insome cases, particles 340 can be further functionalized to chemicallybond to the binder 310. For example, particles 340, such as particle340A, can be surface modified and have reactive functionalities orgroups 360 to chemically bond to binder 310. In such cases, at least asignificant fraction of particles 340 is chemically bound to binder 310.In some cases, particles 340 do not have reactive functionalities tochemically bond to binder 310. In such cases, particles 340 can bephysically bound to binder 310, or binder 310 can encapsulate particles340.

In some cases, some of particles 340 have reactive groups and others donot have reactive groups. For example, in some cases, about 10% ofparticles 340 have reactive groups and about 90% of particles 340 do nothave reactive groups, or about 15% of particles 340 have reactive groupsand about 85% of particles 340 do not have reactive groups, about 20% ofparticles 340 have reactive groups and about 80% of particles 340 do nothave reactive groups, or about 25% of particles 340 have reactive groupsand about 75% of particles 340 do not have reactive groups, about 30% ofparticles 340 have reactive groups and about 60% of particles 340 do nothave reactive groups, about 35% of particles 340 have reactive groupsand about 65% of particles 340 do not have reactive groups, about 40% ofparticles 340 have reactive groups and about 60% of particles 340 do nothave reactive groups, about 45% of particles 340 have reactive groupsand about 55% of particles 340 do not have reactive groups, or about 50%of particles 340 have reactive groups and about 50% of particles 340 donot have reactive groups. In some cases, some of particles 340 may befunctionalized with both reactive and unreactive groups on the sameparticle.

The ensemble of particles 340 may include a mixture of sizes, reactiveand non-reactive particles 340, and different types of particles 340,for example, organic particles including polymeric particles such asacrylics, polycarbonates, polystyrenes, silicones and the like; orinorganic particles such as glasses or ceramics including, for example,silica and zirconium oxide, and the like. In some embodiments, theparticles 340 may have covalently bonded alternating layers and avarying refractive index such as, for example, the particles describedin WO 2016/168147, which is incorporated herein by reference.

Exemplary particles include fumed metal oxides or pyrogenic metaloxides, such as, for example, a fumed silica or alumina. In someembodiments, particles that are highly branched or structured may beused. Such particles prevent efficient packing in the binder matrix andallow interstitial voids or pores to form. Exemplary materials includehighly branched or structured particles include Cabo-Sir fumed silicasor silica dispersions, such as, for example, those sold under tradedesignations TS 520, or pre-dispersed fumed silica particles such asthose available under the trade designation Cabo-Sperse PG 001, PG 002,1020K, 1015 (available from Cabot Corporation). Fumed alumina oxides arealso useful structured particles to form a low refractive index systemalthough silica may be preferred since it has an inherently lowerskeletal refractive index than alumina Examples of alumina oxide areavailable under the trade name Cabo-Sperse, such as, for example, thosesold under the trade designation Carbo-Sperse PG003 or Cabot Spec-A1from Cabot Corp. In some embodiments, aggregates of these exemplaryfumed metal oxides include a plurality of primary particles in the rangeof about 8 nm to about 20 nm and form a highly branched structure with awide distribution of sizes ranging from about 80 nm to greater than 300nm. In some embodiments, these aggregates pack randomly in a unit volumeof a coating to form a mesoporous structure with complex bi-continuousnetwork of channels, tunnels, and pores which entrap air in the networkand thus lower the density and refractive index of the coating. Otheruseful porous materials are derived from naturally occurring inorganicmaterials such as clays, barium sulfates, aluminum, silicates and thelike. The low refractive index layer has an effective refractive indexof 1.23 or less when the metal oxide is silica oxide and 1.33 or lessthen the metal oxide is alumina oxide.

Fumed silica particles can also be treated with a surface treatmentagent. Surface treatment of the metal oxide particles can provide, forexample, improved dispersion in the polymeric binder, altered surfaceproperties, enhanced particle-binder interactions, and/or reactivity. Insome embodiments, the surface treatment stabilizes the particles so thatthe particles are well dispersed in the binder, resulting in asubstantially more homogeneous composition. The incorporation of surfacemodified inorganic particles can be tailored, for example, to enhancecovalent bonding of the particles to the binder, thereby providing amore durable and more homogeneous polymer/particle network.

The preferred type of treatment agent is determined, in part, by thechemical nature of the metal oxide surface. Silanes are preferred forsilica and other siliceous fillers. In the case of silanes, it may bepreferred to react the silanes with the particle surface beforeincorporation into the binder. The required amount of surface modifieris dependent upon several factors such as, for example, particle size,particle type, modifier molecular weight, and/or modifier type. Thesilane modifier can have reactive groups that form covalent bondsbetween particles and the binder, such as, for example, carboxy,alcohol, isocynanate, acryloxy, epoxy, thiol or amines. Conversely, thesilane modifier can have non-reactive groups, such as, for example,alkyl, alkloxy, phenyl, phenyloxy, polyethers, or mixtures thereof. Suchnon-reactive groups may modify the surface of the coatings to improve,for example, soil and dirt resistance or to improve static dissipation.Commercially available examples of a surface modified silica particleinclude, for example, are those available from Cabot Corp. under thetrade designation Cabo-Sil TS 720 and TS 530. It may sometimes bedesirable to incorporate a mixture of functional and non-function groupson the surface of the particles to obtain a combination of thesedesirable features.

Representative embodiments of surface treatment agents suitable for usein the compositions of the present disclosure include, for example,N-(3-triethoxysilylpropyl)methoxyethoxyethoxyethyl carbamate,N-(3-triethoxysilylpropyl)methoxyethoxyethoxyethyl carbamate,3-(methacryloyloxy)propyltrimethoxysilane,3-acryloxypropyltrimethoxysilane,3-(methacryloyloxy)propyltriethoxysilane,3-methacryloyloxy)propylmethyldimethoxysilane,3-(acryloyloxypropyl)methyldimethoxysilane,

-   3-methacryloyloxy)propyldimethylethoxysilane,-   3-methacryloyloxy)propyldimethylethoxysilane,    vinyldimethylethoxysilane, phenyltrimethoxysilane,    n-octyltrimethoxysilane, dodecyltrimethoxysilane,    octadecyltrimethoxysilane,-   propyltrimethoxysilane, hexyltrimethoxysilane,    vinylmethyldiacetoxysilane, vinylmethyldiethoxysilane,    vinyltriacetoxysilane, vinyltriethoxysilane,    vinyltriisopropoxysilane, vinyltrimethoxysilane,    vinyltriphenoxysilane, vinyltri-t-butoxysilane,    vinyltris-isobutoxysilane, vinyltriisopropenoxysilane, vinyltris    (2-methoxyethoxy)silane, styrylethyltrimethoxysilane,    mercaptopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane,    acrylic acid, methacrylic acid, oleic acid, stearic acid, dodecanoic    acid, 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA),    beta-carboxyethylacrylate (BCEA), 2-(2-methoxyethoxy)acetic acid,    methoxyphenyl acetic acid, and mixtures thereof.

The binder 310 can be or can include any material that may be desirablein an application. For example, in some embodiments, which are notintended to be limiting, the binder 310 can be derived fromthermosetting, thermoplastic, and UV curable polymeric materials.Examples include, but are not limited to, polyvinylalcohol (PVA),polyvinylbutyral (PVB), polyvinyl pyrrolidone (PVP), polyethylene vinylacetate copolymers (EVA), cellulose acetate butyrate (CAB),polyurethanes (PURs), polymethylmethacrylate (PMMA), polyacrylates,epoxies, silicones, and fluoropolymers.

The binders can be soluble in a suitable solvent such as, for example,water, ethyl acetate, acetone, 2-butone, and the like, and can be usedas dispersions or emulsions.

Examples of some commercially available binders useful in the mixturesare those available from Kuraray-USA, Wacker Chemical, Dyneon LLC, andRohm and Haas. Although the binder can be a polymeric system, it canalso be added as a polymerizable monomeric system, such as a UV, orthermally curable or crosslinkable system. Examples of such systemswould be UV polymerizable acrylates, methacrylates, multi-functionalacrylates, urethane-acrylates, and mixtures thereof. Some typicalexamples would be 1,6 hexane diol diacrylate, trimethylol propanetriacrylate, pentaerythritol triacryalate. Such systems are readilyavailable from suppliers such as Neo Res (Newark, Del.), Arkema(Philadelphia, Pa.), or Sartomer (Exton, Pa.). Actinic radiation such aselectron beam (E-beam), gamma and UV radiation are useful methods toinitiate the polymerization of these systems, with many embodimentsutilizing UV active systems. Other useful binder systems can also becationically polymerized, such systems are available as vinyl ethers andepoxides.

The polymeric binders can also be formulated with cross linkers that canchemically bond with the polymeric binder to form a crosslinked network.Although the formation of crosslinks is not a prerequisite for theformation of the porous structure or the low refractive index opticalproperties, it is often desirable for other functional reasons such asto improve the cohesive strength of the coating, adhesion to thesubstrate or moisture, or thermal and solvent resistance. The specifictype of crosslinker is dependent upon the binder used. Typicalcrosslinkers for polymeric binders such as PVA would be diisocyanates,titantates such as those available under the trade designation TYZOR-LAf from DowDuPont, Midland, Mich., poly(epichlorhydrin)amide adducts suchas PolyCup 172, (available from Hercules, Wilmington, Del.),multi-functional aziridines such as CX100 (available from Neo-Res,Newark, Del.) and boric acid, diepoxides, diacids and the like.

The polymeric binders may form a separate phase with the particleaggregates or may be inter-dispersed between the particle aggregates ina manner to “bind” the aggregates together into a structures thatconnect with the metal oxidize particles through direct covalent bondformation or molecular interactions such as ionic, dipole, van Der Waalsforces, hydrogen bonding and physical entanglements with the metaloxides.

Optical film 300 can be produced using any method that may be desirablein an application. Generally, in one process, first a solution isprepared that includes a plurality of particles 340, such asnanoparticles, and a polymerizable material dissolved in a solvent,where the polymerizable material can include, for example, one or moretypes of monomers. Next, the polymerizable material is polymerized, forexample by applying heat or light, to form an insoluble polymer matrixin the solvent. In one example, the polymerization occurs in anenvironment that has an elevated level of oxygen adjacent one of thesurfaces, inhibiting the polymerization near that surface to create agradient optical film. In one example, a concentration of photoinitiatornear one of the surfaces is increased relative to another surface, tocreate a gradient optical film.

In some cases, after the polymerization step, the solvent may stillinclude some of the polymerizable material, although at a lowerconcentration. Next, the solvent is removed by drying or evaporating thesolution resulting in optical film 300 that includes a network, or aplurality, of voids 320 dispersed in polymer binder 310. Optical film300 further includes plurality of particles 340 dispersed in thepolymer. Particles 340 are bound to binder 310, where the bonding can bephysical or chemical, or be encapsulated by binder 310.

The porous material 300A can have other materials in addition to binder310 and particles 340. For example, porous polymeric film 300 caninclude one or more additives, such as for example, coupling agents, tohelp wet the surface of a substrate, not expressly shown in FIG. 1, onwhich the layer 300 is formed. As another example, the porous layer 300Acan include one or more colorants, such a carbon black, for imparting acolor, such as the black color, to the layer. Other exemplary materialsin the layer of the porous material 300A include initiators, such as oneor more photo-initiators, anti-stats, UV absorbers and release agents.In some cases, the layer 300A can include a down converting materialthat is capable of absorbing light and reemitting a longer wavelengthlight. Exemplary down-converting materials include phosphors.

In general, porous layer 300A 300 can have a desirable porosity for anyweight ratio of binder 310 to plurality of particles 340. Accordingly,in general, the weight ratio can be any value that may be desirable inan application. In some cases, the weight ratio of binder 310 toplurality of particles 340 is not less than about 1:2.5, not less thanabout 1:2.3, not less than about 1:2, not less than about 1:1, not lessthan about 1.5:1, not less than about 2:1, not less than about 2.5:1,not less than about 3:1, not less than about 3.5:1, not less than about4:1, or not less than about 5:1. In some cases, the weight ratio is in arange from about 1:2.3 to about 4:1.

In some cases, top major surface 332 of the layer of the porous material300A can be treated to, for example, improve the adhesion of opticalfilm 300 to another layer. For example, top major surface 332 can becorona treated.

FIGS. 1B-1G are schematic side-views of a gradient porous layers300B-300G, respectively, according to different aspects of thedisclosure. For clarity, the numbered elements 310-360 and the sizesd₁-d₃ described for FIG. 1A are not shown in FIGS. 1B-1G; however, eachof the descriptions provided for gradient porous materials 300A of FIG.1A also correspond to the gradient porous layers 300B-300 of FIGS.1B-1G, respectively. For example, suitable techniques for creating thegradient porous materials 300B-300G are described, for example, in WO2011/050232.

In FIG. 1B, gradient porous layer 300B includes a local volume fractionof interconnected voids 390B that varies along the thickness direction,for example, in a monotonic manner as shown. In one particularembodiment, a first local volume fraction of interconnected voids 370Bproximate a first surface 330B of gradient porous layer 300B is lowerthan a second local volume fraction of interconnected voids 375Bproximate a second surface 332B of the layer 300B.

Gradient porous layer 300B can be prepared using a variety oftechniques, as described elsewhere. In one particular embodiment,gradient porous layer 300B can be prepared, for example, using anabsorbance based technique where the intensity of polymerization lightdecreases from first surface 330B to second surface 332B.

In FIG. 1C, gradient porous layer 300C includes a local volume fractionof interconnected voids 390C that varies along the thickness direction,for example, in a step-wise manner as shown. In one particularembodiment, a first local volume fraction of interconnected voids 370Cproximate a first surface 330C of gradient porous layer 300C is lowerthan a second local volume fraction of interconnected voids 375Cproximate a second surface 332C of the layer 300C. In some cases, forexample, shown FIG. 1C, first local volume fraction of interconnectedvoids 370C transitions sharply (that is, step-wise) to second localvolume fraction of interconnected voids 375C. In some cases, a thicknesst₂ of the second volume fraction of interconnected voids 375C can be asmall percentage of the total thickness t₁, for example, from about 1%to about 5%, or to about 10%, or to about 20%, or to about 30% or moreof the total thickness t₁.

The gradient porous layer 300C can be prepared using a variety oftechniques, as described elsewhere. In one particular embodiment, thegradient porous layer 300C can be prepared, for example, by using adifference in the polymerization initiator concentration or a differencein the polymerization inhibitor concentration proximate the first andsecond surfaces (330C, 332C).

In FIG. 1D, gradient porous layer 300D includes a local volume fractionof interconnected voids 390D that varies along the thickness direction,for example, having a minimum local volume fraction of interconnectedvoids 377D as shown. In one particular embodiment, a first local volumefraction of interconnected voids 370D proximate a first surface 330D ofgradient porous layer 300D is approximately the same as a second localvolume fraction of interconnected voids 375D proximate a second surface332D of the film 300D. In some cases, for example, shown FIG. 1D, firstlocal volume fraction of interconnected voids 370D transitions sharply(that is, step-wise) to minimum local volume fraction of interconnectedvoids 377D. In some cases, a thickness t₂ of the minimum volume fractionof interconnected voids 377D can be a small percentage of the totalthickness t₁, for example, from about 1% to about 5%, or to about 10%,or to about 20%, or to about 30% or more of the total thickness t₁. Insome cases, the relative position of the minimum local volume fractionof interconnected voids 377D can be located anywhere, for example, atthickness t₃ from first surface 330D, within gradient porous layer 300D.

Gradient porous layer 300D can be prepared using a variety oftechniques, as described elsewhere. In one particular embodiment, theporous polymeric optical film 300D can be prepared, for example, bylaminating a pair of the gradient optical films 300C shown in FIG. 1C toeach other, along the second surfaces 332C.

In FIG. 1E, gradient porous layer 300E includes a local volume fractionof interconnected voids 390E that varies along the thickness direction,for example, having a step-change local volume fraction ofinterconnected voids proximate a first and a second surface 330E, 332E,as shown. In one particular embodiment, a first local volume fraction ofinterconnected voids 370E proximate a first surface 330E of porouspolymeric optical film 300E is approximately the same as a second localvolume fraction of interconnected voids 375E proximate a second surface332E of the film 300E. In some cases, for example, shown FIG. 1E, firstlocal volume fraction of interconnected voids 370E transitions sharply(that is, step-wise) to maximum local volume fraction of interconnectedvoids 377E. In some cases, a thickness t₂ and t₃ of the first and secondlocal volume fraction of interconnected voids 370E and 375E,respectively, can be a small percentage of the total thickness t₁, forexample, from about 1% to about 5%, or to about 10%, or to about 20%, orto about 30% or more of the total thickness t₁. In some cases, each ofthe first and second local volume fraction of interconnected voids 370Eand 375E can have transitions that are not step-wise (not shown, butsimilar to the monotonic variation shown in FIG. 1B).

Gradient porous layer 300E can be prepared using a variety oftechniques, as described elsewhere. In one particular embodiment,gradient porous layer 300E can be prepared, for example, by laminating apair of the porous polymeric optical films 300C shown in FIG. 1C to eachother, along the first surfaces 330C.

In FIG. 1F, gradient porous layer 300F includes a local volume fractionof interconnected voids 390F that varies along the thickness direction,for example, having a gradient minimum local volume fraction ofinterconnected voids 377F as shown. In one particular embodiment, afirst local volume fraction of interconnected voids 370F proximate afirst surface 330F of gradient porous layer 300F is approximately thesame as a second local volume fraction of interconnected voids 375Fproximate a second surface 332F of the film 300F. In some cases, forexample, shown FIG. 1F, first local volume fraction of interconnectedvoids 370F transitions gradually (that is, in a monotonic gradient) to aminimum local volume fraction of interconnected voids 377F, and againtransitions gradually to the second volume fraction of interconnectedvoids 375F.

Gradient porous layer 300F can be prepared using a variety oftechniques, as described elsewhere. In one particular embodiment,gradient porous layer 300F can be prepared, for example, by laminating apair of the gradient porous layers 300B shown in FIG. 1B to each other,along the second surfaces 332B.

In FIG. 1G, gradient porous layer 300G includes a local volume fractionof interconnected voids 390G that varies along the thickness direction,for example, having a pair of step-change local volume fraction ofinterconnected voids 377G, 378G, as shown. In one particular embodiment,a first local volume fraction of interconnected voids 370G proximate afirst surface 330G of gradient porous layer 300G is approximately thesame as a second local volume fraction of interconnected voids 375Gproximate a second surface 332G of the film 300G. In some cases, forexample, shown FIG. 1G, first local volume fraction of interconnectedvoids 370E transitions sharply (that is, step-wise) to minimum localvolume fraction of interconnected voids 377G, transitions sharply againto a maximum local volume fraction of interconnected voids 380G,transitions sharply again to a minimum local volume fraction ofinterconnected voids 378G, and finally transitions sharply yet again tothe second local volume fraction of interconnected voids 375G. In somecases, each of the local volume fraction of interconnected voids canhave transitions that are not step-wise (not shown, but similar to themonotonic variation shown in FIG. 1B).

Gradient porous layer 300G can be prepared using a variety oftechniques, as described elsewhere. In one particular embodiment,gradient optical film 300G can be prepared, for example, by a multilayercoating technique, where a different photoinitiator concentration can beused in strata corresponding to minimum local void volume fraction(377G, 378G) than in strata corresponding to maximum local void volumefraction 390G. In one particular embodiment, gradient optical film 300Gcan be prepared, for example, by a multilayer coating technique, wherethe strata include different ratios of polymeric binder to particles.

FIG. 3 is a schematic cross-sectional view of an optical construction360, which includes a porous polymeric film 380 disposed on a substrate370. The porous polymeric film 380 can be include single or multiplelayers, where each layer may be the same or different. In some cases,the porous polymeric film 380 may be coated directly onto substrate 370.In some cases, the porous polymeric film 380 may be first formed andthereafter transferred onto substrate 370, which can be translucent,transparent, or opaque.

The substrate 370 can be or can include any material that may besuitable in an application, such as a polymeric material (for example, abiocompatible plastic for a medical device), a dielectric, asemiconductor, or a conductor (such as a metal). For example, thesubstrate 370 can include or be made of glass and polymers such aspolyethylene terephthalate (PET), polycarbonates, and acrylics. In somecases, substrate 370 can include a polarizer such as a reflectivepolarizer, an absorbing polarizer, a wire-grid polarizer, or a fiberpolarizer. In some case, substrate 370 can include multiple layers. Insome cases, substrate 370 can include a structured surface, such as asurface having a plurality of microstructures.

In some embodiments, the substrate 370 is a release liner that maythereafter be stripped away from a surface 384 of the porous polymericfilm 380 to expose a major surface 384 of the porous polymeric film 380that can, for example, be bonded to another substrate or surface. Insome embodiments, which are not intended to be limiting, the releaseforce for releasing porous polymeric film 380, which can be a low indexlayer, from a release liner 370 is generally less than about 200g-force/inch, or less than about 150 g-force/inch, or less than about100 g-force/inch, or less than about 75 g-force/inch, or less than about50 g-force/inch.

In some embodiments, the substrate 370 is a fiber polarizer, whichincludes a plurality of substantially parallel fibers that form one ormore layers of fibers embedded within a binder with at least one of thebinder and the fibers including a birefringent material. Thesubstantially parallel fibers define a transmission axis and areflection axis. The fiber polarizer substantially transmits incidentlight that is polarized parallel to the transmission axis andsubstantially reflects incident light that is polarized parallel to thereflection axis. A fiber polarizing film is a matrix layer that containsmultiple fibers having internal birefringent interfaces, i.e. interfacesbetween a birefringent material and another material. The parameters ofthe fibers in a fiber polarizer film can be selected to enhancepolarization.

In some cases, substrate 370 can include a partial reflector. A partialreflector is an optical element or a collection of optical elementswhich reflect at least 30% of incident light while transmitting theremainder, minus absorption losses. Suitable partial reflectors include,for example, foams, polarizing and non-polarizing multilayer opticalfilms, microreplicated structures (e.g. BEF), polarized andnon-polarized blends, wire grid polarizers, partially transmissivemetals such as silver or nickel, metal/dielectric stacks such as silverand indium tin oxide, and asymmetric optical films. Perforated partialreflectors or mirrors can also be useful as partial reflectors, such as,for example, those available from 3M under the trade designationEnhanced Specular Reflector (“ESR”).

In addition, asymmetric reflective films may be desirable for certainapplications. In that case, average transmission along one stretchdirection may be desirably less than, for example, 50%, while theaverage transmission along the other stretch direction may be desirablyless than, for example 20%, over a bandwidth of, for example, thevisible spectrum (400-700 nm), or over the visible spectrum and into thenear infrared (e.g., 400-850 nm).

In addition, although partial reflector films and asymmetric reflectivefilms are discussed separately herein, it should be understood that twoor more of such films could be provided to reflect substantially alllight incident on them (provided they are properly oriented with respectto each other to do so). For example, this construction can be used whenoptical film 380 with multiple layers is used as a reflector.

In one example, substrate 370 can be a reflective polarizer. Areflective polarizer layer substantially reflects light that has a firstpolarization state and substantially transmits light that has a secondpolarization state, where the two polarization states are mutuallyorthogonal. For example, the average reflectance of a reflectivepolarizer in the visible for the polarization state that issubstantially reflected by the reflective polarizer is at least about50%, at least about 60%, at least about 70%, at least about 80%, atleast about 90%, or at least about 95%. As another example, the averagetransmittance of a reflective polarizer in the visible for thepolarization state that is substantially transmitted by the reflectivepolarizer is at least about 50%, at least about 60%, at least about 70%,at least about 80%, at least about 90%, at least about 95%, at leastabout 97%, at least about 98%, or at least about 99%. In some cases, thereflective polarizer substantially reflects light having a first linearpolarization state (for example, along the x-direction) andsubstantially transmits light having a second linear polarization state(for example, along the z-direction).

Any suitable type of reflective polarizer may be used such as, forexample, a multilayer optical film (MOF) reflective polarizer such asthose available from 3M under the trade designation VIKUITI DualBrightness Enhancement Film (DBEF), a diffusely reflective polarizingfilm (DRPF) having a continuous phase and a disperse phase, such asthose available from 3M under the trade designation VIKUITI DiffuseReflective Polarizer Film, a wire grid reflective polarizer, or acholesteric reflective polarizer.

For example, in some cases, the reflective polarizer layer can be orinclude an MOF reflective polarizer, formed of alternating layers ofdifferent polymer materials, where one of the sets of alternating layersis formed of a birefringent material, where the refractive indices ofthe different materials are matched for light polarized in one linearpolarization state and unmatched for light in the orthogonal linearpolarization state. In such cases, an incident light in the matchedpolarization state is substantially transmitted through the reflectivepolarizer and an incident light in the unmatched polarization state issubstantially reflected by reflective polarizer. In some cases, an MOFreflective polarizer can include a stack of inorganic dielectric layers.

As another example, the reflective polarizer can be or include apartially reflecting layer that has an intermediate on-axis averagereflectance in the pass state. For example, the partially reflectinglayer can have an on-axis average reflectance of at least about 90% forvisible light polarized in a first plane, such as the xy-plane, and anon-axis average reflectance in a range from about 25% to about 90% forvisible light polarized in a second plane, such as the xz-plane,perpendicular to the first plane.

In some cases, the reflective polarizer can be or include a circularreflective polarizer, where light circularly polarized in one sense,which may be the clockwise or counterclockwise sense (also referred toas right or left circular polarization), is preferentially transmittedand light polarized in the opposite sense is preferentially reflected.One type of circular polarizer includes a cholesteric liquid crystalpolarizer. In some cases, the reflective polarizer can be a multilayeroptical film that reflects or transmits light by optical interference.

In one example, the substrate 370 can have a microstructured surface,such as a prismatic light directing film. For example, the porouspolymeric film 380 can be coated on the prism side of a lightredirecting film such as VIKUITI BEF from 3M. The BEF includes aplurality of linear prisms with, for example, a 24 micron pitch and aprism peak or apex angle of about 90 degrees. The porous polymeric film380 can be coated on the microstructured surface as a conformal coating,a planarized coating, or pattern coated.

In various embodiments, substantial portions of each two neighboringmajor surfaces in optical construction 360 are in physical contact witheach other along the bottom major surface 384 of the porous polymericfilm 380. For example, at least 50%, at least 60%, at least 70%, atleast 80%, at least 90%, or at least 95% of the two neighboring majorsurfaces are in physical contact with each other. For example, in somecases, porous polymeric film 380 is coated directly on substrate 370.

In some embodiments, the major surface 384 of the porous polymeric film380 overlies an optional layer 386, which may in some cases be anadhesive layer, such as, for example, a pressure sensitive adhesivelayer. In some embodiments, the layer 386 may be an optically clearadhesive. In some embodiments, the optional layer 386 may be a tie layeror a primer coating layer that provides compatibility between the porouspolymeric film 380 and the substrate 370. In another embodiment, a majorsurface 382 of the porous polymeric film 380 includes an optional layer388, which may in some cases be an adhesive layer. In some embodiments,one or both of the adhesive layers 386, 388 can be used to provide atransferable porous polymeric film 380, which may be placed in contactwith a substrate or surface.

In some embodiments, one or both of the optional layers 386, 388 may beintervening optical layers between the porous polymeric film 380 and thesubstrate 370, such that the porous polymeric film 380 does not directlycontact the substrate 370. In the present application, the porouspolymeric film 380 may be present “on” or “overlying” an underlyinglayer when the porous polymeric film 380 is in optical communicationwith the underlying layer, and the porous polymeric film 380 need notdirectly contact the underlying layer.

FIG. 4 is a schematic cross-sectional view of an optical construction400. Optical construction 400 can include a porous polymeric film 430disposed on a substrate 410 and an optical adhesive layer 420 disposedon the film 430. Substrate 410 can be any of the substrates describedelsewhere, including, for example, a substrate such as substrate 370described with reference to FIG. 3. In some cases, the optical adhesivelayer 420 can act as a sealer to inhibit infiltration of voids of theporous polymeric film 430 (similar to seal layer 1206 of FIG. 12Adiscussed below). In some cases, it may be desirable to have adhesivelayer 420 and porous polymeric film 430 on opposite sides of thesubstrate 410. In other cases, it may be desirable to have the porouspolymeric film 430 on both sides of substrate 410.

The optical adhesive layer 420 can be any optical adhesive that may bedesirable and/or available in an application, and should be ofsufficient optical quality and light stability such that, for example,the adhesive layer does not yellow with time or upon exposure to weatherso as to degrade the optical performance of the adhesive and opticalfilm 300. In some cases, the optical adhesive layer 420 can be asubstantially clear optical adhesive meaning that the adhesive layer hasa high specular transmittance and a low diffuse transmittance. Forexample, in such cases, the specular transmittance of optical adhesivelayer 420 is not less than about 70%, not less than about 80%, not lessthan about 90%, or not less than about 95%.

FIG. 5 is a schematic view of a stack 500 of materials thatschematically illustrates various embodiments of optical filmconstructions in which the porous polymeric films of FIGS. 2A-2G, andoptical film constructions of FIGS. 3-4, can be used as fluid sensors,optical switches, and the like. The stack 500 includes a first layer502, a porous polymeric film 504 such as described above, and a secondlayer 506. The appearance of the stack 500 can change based on thediffusive properties of the porous polymeric film 504. In someembodiments, an optical absorber can be placed in the porous polymericfilm 504, in a fluid that fills the porous polymeric film 504, in asurface layer on (or proximate) either surface of porous polymeric film504, or in the fluid being monitored by the stack 500.

In some embodiments, a selected portion of the porous polymeric film canbe filled with a filler material, while leaving other portions of thefilm remain unfilled and available for fluid sensing. Many differentfilling patterns are possible. For example, in one embodiment that isnot intended to be limiting, first region can be filled with a fillermaterial, leaving an open second region of unfilled porous materialtherebetween. When the porous polymeric film is used for fluid sensing,a fluid sensing region is confined to the open second region, which canbe positioned around or between the first regions of the fillermaterial. In various embodiments, which are not intended to be limiting,the filler material in first regions of the porous polymeric film can beclear, colored, black or white.

The first layer 502 and the second layer 506 on the opposed first andsecond major surfaces of the optical film 504 can be made of the same ordifferent materials, as illustrated in more detail below. In someembodiments, which are not intended to be limiting, the layers 502, 506are polymeric films. The layers of the stack 500 can be in opticalcommunication but do not need to be in direct physical contact. In someexamples, intervening layers 505, 507 can reside between layers of stack500, which can be the same or different. The intervening layers 505, 507can vary widely, and some examples include, but not limited to,polymeric films, glass, adhesives, tie or primer layers, air, and thelike. In some embodiments, spaces between the layers of the stack 500can enable ingress or egress of liquid from the stack 500, or canprovide a desired optical effect. In some examples, layers of the stack500, including first layer 502, optical film 504, and second layer 506,can directly contact each other such that the first layer 502 resides ona first major surface 509 of the optical film 504 and the second layer506 resides on a second major surface 511 of the optical film 504.

In one embodiment, the first layer 502 is transparent or translucent,and the second layer 506 is pigmented. If the stack 500 is viewedthrough the first layer 502, and fluid is present is present in theporous polymeric film layer 504, the porous polymeric film layer appearstransparent or translucent, and the stack 500 appears to an observer tohave the pigmented color of the second layer 506. When the fluid isabsent from the optical layer 504, the porous polymeric film 504 isopaque, and the stack 500 appears white to the observer viewing thestack through the first layer 502. This change of appearance can beconfigured for the entire stack 500, or for selected subregions thereof.

In another embodiment, the first layer 502 is a first pigmented color,and the second layer 506 is a second pigmented color different from thefirst pigmented color, or a dyed color different from the firstpigmented color. When the stack 500 is viewed through first layer 502,if fluid is present is present in the porous polymeric film layer 504,the porous polymeric film 504 is substantially transparent ortranslucent, and the stack 500 appears to take on the combination of thefirst and the second colors from the first layer 502 and the secondlayer 506. When the fluid is absent from the porous polymeric film 504,the porous polymeric film 504 is substantially opaque, and the stack 500appears to an observer to have the color of the first layer 502.

In other embodiments, the first layer 502 can be an interferencereflector such as, for example, a multilayered polymeric film, and thesecond layer 506 can be omitted. In another example, the first layer 502can be a first interference reflector and the second layer 506 can be asecond interference reflector different from the first interferencereflector. Suitable interference reflectors include, but are not limitedto, multilayered polymeric films, inorganic multilayer films, andorganic/inorganic hybrid multilayer films.

In another embodiment, the first layer 502 can include a frequencydown-converting material, and the second layer 506 can be dyed,pigmented, or be an interference reflector. Suitable down-convertingmaterials are capable of absorbing light and reemitting a longerwavelength light, and exemplary down converting materials include, butare not limited to, phosphors, material layers including fluorescingmaterials or chemistries, quantum dots, and the like.

In another embodiment, either or both of the first layer 502 and thesecond layer 506 may include an indicia alone or in combination with thepigments and dyes described above. Suitable indicia include, but are notlimited to, text, machine readable codes such as bar codes and QR codes,symbols, colors, a selected wavelength, and combinations thereof. Forexample, if the first layer 502 is transparent or translucent, thesecond layer 506 may include an indicia. If the stack 500 is viewedthrough the first layer 502, and fluid is present in the porouspolymeric film layer 504, the layer 504 appears transparent ortranslucent, and the indicia in the second layer 506 is visible orotherwise detectable with an appropriate detector. When the fluid isabsent from the porous polymeric layer 504, the layer 504 is opaque, thestack 500 appears white, and the indicia is not visible or detectable.The stack 500 can be configured to show this change of appearance in itsentirety, or in one or more selected subregions thereof.

In another embodiment, a surface underlying the optical stack caninclude a colored region, an indicia, or a combination thereof. Thepresence or absence of fluid in the porous polymeric film layer cancause the optical stack 500 to be transmissive, revealing to an observerthe underlying color or indicia, or opaque, obscuring the underlyingcolor or indicia. The optical stack 500 can be configured to show thischange of appearance in its entirety, or in one or more selectedsubregions thereof.

In some embodiments, the fluid sensing porous layers described hereincan be applied as a layer to a surface, or provided in the form of afilm that is bonded to a surface, to form a fluid sensor thereon.

For example, in some embodiments the fluid sensors including the porouslayers applied on an interior of a closure device including a liquid.The porous layers of the fluid sensors may be used to provide a rapidvisual indication of the presence or absence of a fluid in the closuredevice. The closure device may be removably attached to a wide varietyof articles such as, for example, a medical device, a packaging device,and the like.

In one embodiment, the porous layers are applied on an interior surfaceof the closure device, as shown in FIGS. 6A-C. Any of the closuredevices shown in FIGS. 6A-C may further include an attachment means suchas, for example, threads, or a snap-on mechanism for attaching theclosure device to an article. These attachments mechanisms are omittedfrom FIGS. 6A-E for clarity.

The closure devices 600A-C include a body 601A-C with a fluid sensor602A-C disposed on at least a portion of a respective interior surface610A-C thereof. In some embodiments, the body 601A-C may be a polymericmaterial or glass that is transparent or translucent to at least onewavelength of visible light. The fluid sensors 602A-C may include asingle layer of the porous material described in FIG. 2, or a stack oflayers including a layer of the porous material (FIGS. 3-5). When viewedthrough the transparent or translucent body 601A-C, a change in theappearance of the fluid sensor 602A-C can provide a visual indication ofthe presence or absence of a fluid within the closure member 600A-C.

Referring to FIG. 6A, in one embodiment the closure member 600A includesa transparent, translucent, or opaque body 601A that includes aninterior chamber 607A with an interior surface 610A. A fluid sensor 602Ais present on the interior surface 610A at an end portion 603A of thebody 601A. The fluid sensor 602A includes an open region 605 such thatthe fluid sensor 602A has a ring-like shape.

The closure device 600A further includes a vent 632A that provides anopen path from the fluid sensor 602A to an exterior of the body 601A. Ifthe fluid sensor 602A contacts a fluid, as the fluid evaporates toatmosphere via the vent 632A, the appearance of the optical fluid sensor602A changes in a manner that is detectable to an observer when thefluid sensor 602A is viewed through the body 601A or through the openinterior chamber 607A. All or a portion of the closure device 600A canbe transmissive to visible light, and the visible light transmissiveregions allow optical inspection (visual or by machine) of the fluidsensor 602A.

In some embodiments, the closure member 600A includes an optionalsealing member such as, for example, a foil packaging layer 630A, whichprevents evaporation of the fluid from the closure member 600A prior touse. For example, the foil packaging layer 630A can be adhered to thebody 601A with a layer of an adhesive (not shown in FIG. 6A), and can bepeeled away from the body 601A when the closure member 600A is ready foruse.

In another example shown in FIG. 6B, a closure member 600B includes afluid sensor 602B that completely covers or substantially covers aninterior surface 610B of an end portion 603B of the transparent ortranslucent body 601B. The closure device 600B further includes a vent632B that provides an open path from the fluid sensor 602B to anexterior of the body 601B. If the fluid sensor 602B contacts a fluid, asthe fluid evaporates to the atmosphere via the vent 632B, the appearanceof the optical fluid sensor 602B changes in a manner that is detectableto an observer when the fluid sensor 602B is viewed through the body601B or through the open interior chamber 607B. All or a portion of theclosure device 600B can be transmissive to visible light, and thevisible light transmissive regions allow optical inspection (visual orby machine) of the fluid sensor stacks 602A.

In some embodiments, the closure member 600B includes an optionalsealing member such as, for example, a foil packaging layer 630B, whichprevents evaporation of the fluid from the closure member 600B prior touse.

In another example shown in FIG. 6C, a closure member 600C includes atransparent or translucent body 601C in which a fluid sensor 602Ccompletely covers or substantially covers an interior surface 610C of anend portion 603C, as well as a side portion 612C of the body 601C. Theembodiment of FIG. 6C does not include a vent, as a threaded closuremember in itself is inherently self-vented, because it is difficult tomaintain a permanent liquid-tight seal between the closure member and amedical device on which the closure member is applied.

In another embodiments, the fluid sensor is not on the body of theclosure member, but is on a component inside the closure member.

For example, in an embodiment shown in FIG. 6D, a closure member 600Dincludes a body 601D with walls 603D. The walls 603D include anattachment mechanism 670D such as for example, an arrangement of threadsor a snap-on ring, for attaching the body 601D to an article. The walls603D further include a vent 642D that allows a fluid 640D within acavity 672D of the closure device to gradually evaporate.

A plunger 650D is moveable within a bore 671D formed by the cavity 672Dwithin the walls 603D of the body 601D. The plunger 650D includes aplunger body 652D that is moveable with the bore 671D. The plunger body652D has thereon a fluid sensor 654D, which may include, for example, acoating of a porous material described above deposited on the plungerbody 652D, or an optical film stack including a layer of the porousmaterials described above that is adhered to the plunger body 652D. Asthe plunger 650D moves along the bore 671D in the direction of the arrowA and displaces the fluid 640D, the fluid 640D moves around the plunger650D and contacts the porous material 654D. A change in the appearanceof the porous material 654D can provide a rapid visual indication of thepresence or absence of the fluid 640D in the closure device 600D.

For example, if the walls 603D are transmissive to a selected wavelengthof light, and the plunger 650D is colored or includes an indicia, thepresence or absence of the fluid 640D in the closure device can bemonitored by observing the porous material 654D. In one exampleembodiment, if an observer views the closure device along the directionA, and the fluid 640D is present, the porous material 654D will betransparent or translucent, and the color of the plunger body 652D orthe indicia thereon will be readily visible. If the fluid 640D is notpresent, the porous material 654D will be white or opaque, which willobscure the plunger 652D and any indicia thereon. A change in theappearance of the porous material 654D can provide a rapid visualindication of the presence or absence of the fluid 640D in the closuredevice 600D, and at an interface between the plunger and a medicaldevice.

In another embodiment shown in FIG. 6E, a closure member 600E includes abody 601E with walls 603E. The walls 603E include an attachmentmechanism 670E such as for example, an arrangement of threads or asnap-on ring, for attaching the body 601E to an article such as, forexample, a medical device. The walls 603E further include a vent 642Ethat allows a fluid 640E within a fluid reservoir 680E of the closuredevice to gradually evaporate. In the embodiment of FIG. 6E, the fluidreservoir 680E is an absorbent material such as, for example, apolymeric foam, for retaining the fluid 640E.

The fluid reservoir 680E resides at least partially within a fluidsensor 654E, which is on an interior surface 610E of the walls 603E ofthe body 601E. In various embodiments, the fluid sensor 654E mayinclude, for example, a coating of a porous material described abovedeposited on the interior surface 610E, or an optical film stackincluding a layer of the porous materials described above that isadhered to the interior walls 610E.

As the fluid 640E evaporates via the vent 642E, the fluid 640E isdepleted in the fluid reservoir 680E, as well as in the fluid sensor654E, and the presence or absence of fluid causes a change in theappearance of the fluid sensor 654E, which can provide a rapid visualindication of the presence or absence of the fluid in the closure member600E.

In one example embodiment, if an observer views the closure device 600Ethrough the walls 603E, which are transparent or translucent to at leastone wavelength of light, if fluid is present in the porous material ofthe fluid sensor 654E, the porous material will be transparent, whilethe absence of fluid results in a color change of the porous material towhite or opaque. In one embodiment, the fluid reservoir 680E may becolored or include an indicia, and the change in appearance of theporous material in the fluid sensor 654E caused by the presence orabsence of fluid may reveal the color or indicia.

In some examples, which are not intended to be limiting, the closuredevices 600 can be impregnated with an antimicrobial or disinfectingfluid. Suitable antimicrobial fluids include, but not limited to,isopropyl alcohol, ethyl alcohol, chlorhexidine gluconate (CHG),chloroxylenol (PCMX), biguanides such as, for example, polyhexamethylenebiguanide (PHMB), bisbiguanides, polymeric biguanides, povidone iodine,hydrogen peroxide, octenidine, benzalkonium chloride, alexidinedihydrochloride, cetyl pyridinium chloride, antimicrobially effectivesalts thereof, and mixtures and combinations thereof.

In some embodiments, which are not intended to be limiting, the closuredevices 600A-E can be applied on a medical device such as, for example,a needleless connector, a stopcock, a male luer of an IV set, astethoscope, or the like, to provide passive disinfection of the medicaldevice. As the level of the antimicrobial liquid contacting the fluidsensors 602A-E changes, the appearance of the sensors 602A-E changes,which can provide a visual indication of the presence or absence of thedisinfecting fluid remaining in the closure member. The change in theappearance of the fluid sensors may be used to alert medical personnelthat the closure devices are no longer capable of performing an adequateantimicrobial or disinfecting function, and should be replaced tomaintain the sterility of the underlying medical device.

In one embodiment illustrated schematically in FIG. 7, an optical fluidfilm sensor stack 700 includes a transparent or translucent cover layer702, a porous layer 704, and a functional layer 706. In variousembodiments, the functional layer 706 can be a layer of a foamedmaterial that is capable of absorbing an evaporative fluid, may be apigmented material, or may include an indicia, or any combinationthereof. The optical fluid sensor stack 700 further includes an adhesivelayer 708, which in some non-limiting example embodiments is a pressuresensitive adhesive.

The optical fluid sensor stack 700 may be applied on any surface suchas, for example, an interior surface of a body of a closure member, oron a plunger, as shown in FIGS. 6A-6E. The optical fluid sensor stack700 includes a layer 704 of a porous material such as, for example, aporous polymeric film. Depending on the presence of an evaporativeliquid in the porous layer 704, the appearance of the optical fluid filmsensor stack 700 changes. For example, when the stack 700 is viewedthrough the first layer 702 and a fluid is present, the porous layer 704is transparent or translucent, and the stack 700 appears to have thepigmented color of the underlying functional layer 706, or an indicia inthe layer 706, or on the body of the closure member to which the stackis attached (or both), is apparent to the observer. When the fluid isabsent, the porous layer 704 is opaque, which obscures the layer 706,and the stack appears white. As noted above, this change of appearancecan be for the entire stack or a portion thereof, and can provide arapid visual indication of the presence or absence of fluid remainingthe cap. For example, in one embodiment, if the optical fluid sensorstack appears white, an antimicrobial fluid is no longer contacting theporous layer 704, and the closure member may need to be discarded andreplaced with a new closure member having an optical stack with acolored appearance.

As will be apparent to one of ordinary skill, the optical fluid filmsensor stacks 700 can be disposed on a variety of other enclosures orsurfaces to provide a rapid visual indication of the presence or absenceof fluid on or within the enclosure. In one example, the optical fluidfilm sensor stacks 700 can be applied on an interior surface of a foodpackaging film or food packaging container to provide an indication ofmoisture intrusion, which may in some cases be indicative of thefreshness of the contents thereof. In another example, the optical filmstacks could be applied to a surface of a personal care article, amedical article such as a bandage, and the like, to provide anindication of the presence of moisture at the surface.

In another example embodiment, of the optical fluid film sensor stack700 can be attached to a final product or a subassembly product in amanufacturing process to provide a rapid visual or machine readableindication of the presence or absence of water contamination, or otherenvironmental conditions. In some examples, the change of appearance ofthe optical fluid film sensor stack 700 could be used as part of asupply chain quality control.

In another example embodiment, one or more components of the opticalstack 700 of FIG. 7 can be used as a switchable light extraction layeralong an interface between the stack 700 and a surface of an opticalcomponent. In one example shown in FIG. 8A, which is not intended to belimiting, a light guide configuration 810 includes a light extractionlayer 800A with transparent or translucent light scattering layer 802,and a porous polymeric film layer 804. The light extraction layer 800Ais applied on a light guide 812. The configuration 810 further includesa light source 820 that emits light into a surface 821 of the lightguide 812. Suitable light sources 820 include light emitting diodes(LEDs), lasers, and the like. In an example embodiment, the lightscattering layer 802 can be fluorescent, and the light source 808 can bea light emitting diode (LED), such as a blue LED. The porous polymericfilm layer 804 is in optical contact with light guide 812, and in someexample embodiments may be attached via a an optically clear adhesivelayer (not shown in FIG. 8A).

In FIG. 8A, the porous polymeric film 804 is free or substantially freeof liquid. In some examples, the porous polymeric film 804 is a lowrefractive index material that serves as a cladding on the lightguide812 and as shown by the arrows 830 can cause light travelling within thelightguide 812 to be total internally reflected along a surface 814 whenthe porous polymeric film 804 is substantially free of liquid. In theembodiment of FIG. 8A, the porous polymeric film 804 reflects all orsubstantially all of the light at the surface 814, and light within thelightguide 812 will not be transmitted to the scattering layer 802.

Referring now to FIG. 8B, a light guide configuration 850 includes alight extraction layer 800B with transparent or translucent lightscattering layer 852, and a porous polymeric film layer 854. The lightextraction layer 800B is applied on a light guide 862. The configuration850 further includes a light source 870 that emits light into a surface871 of the light guide 862. The porous polymeric film 854 contains afluid, which reduces the refractive index of the film 854, and allowslight extraction from the surface 864 thereof. As shown by the arrow880, light within the lightguide 862 is extracted at the surface 864,passes through the porous polymeric film layer 854, which is transparentor translucent, enters the scattering layer 852, and as shown by thearrows 882 can be viewed by an observer. In one example embodiment, ifthe scattering layer 802 is configured to include a fluorescentmaterial, the lightguide 862 will have a glowing appearance when theporous polymeric film layer 854.

In another embodiment shown in FIG. 9A, a light guide configuration 910includes a light extraction layer 900A with transparent or translucentlight scattering layer 902 on a first major surface 914 of a light guide912, and a porous polymeric film layer 904 on an opposed second majorsurface 915 of the light guide 912. The configuration 910 furtherincludes a light source 920 that emits light into a surface 921 of thelight guide 912. In one example embodiment, the light scattering layer902 can include a fluorescent material, and the light source 920 can bea light emitting diode (LED), such as a blue LED.

The scattering layer 902 and the porous polymeric film layer 904 are inoptical contact with the first major surface 914 and the second majorsurface 915 of the light guide 912, respectively, and in some exampleembodiments may be attached via a layer of an optically clear adhesive(not shown in FIG. 9A). A major surface 917 of the porous optical filmlayer 904 includes a light absorbing layer 916 thereon.

In FIG. 9A, as shown by the arrows 930, if the porous polymeric filmlayer 904 is substantially free of fluid, when light is emitted by thelight source 920 into the light guide 912, the porous polymeric filmlayer 904 is substantially opaque. The light 930 is totally reflectedwithin the light guide 912, and enters the scattering layer 902. Asshown by the arrows 932, the light traversing the scattering layer 902will be viewable by an observer, and in embodiments in which thescattering layer includes a fluorescent material, the light guideconfiguration 910 will appear to glow. The porous polymeric film layer904 thus isolates any light travelling within the light guide 912 fromthe light absorbing layer 916, and ensures that the light with the lightguide 912 therein will be transmitted to the scattering layer 902.

Referring now to FIG. 9B, a light guide configuration 950 includes alight extraction layer 900B with a transparent or translucent lightscattering layer 952 on a first major surface 964 of a light guide 962,and a porous polymeric film layer 954 on an opposed second major surface965 of the light guide 962. The configuration 950 further includes alight source 970 that emits light into a surface 971 of the light guide962. In one example embodiment, the light scattering layer 952 can befluorescent, and the light source 970 can be a light emitting diode(LED), such as a blue LED.

The scattering layer 952 and the porous polymeric film layer 954 are inoptical contact with the first major surface 964 and the second majorsurface 965 of the light guide 962, respectively, and in some exampleembodiments may be attached via a an optically clear adhesive layer (notshown in FIG. 9B). A major surface 967 of the porous optical film layer954 includes a light absorbing layer 966 thereon.

In FIG. 9B, as shown by the arrow 980, if the porous polymeric filmlayer 954 is includes a fluid, when light is emitted by the light source970 into the light guide 962, the porous polymeric film layer 954 istransmissive, and the light 980 exits the light guide 962 at the surface969 and enters the porous polymeric film layer 954, which allows thelight 980 to be absorbed by the light absorbing layer 966. As shown bythe arrows 982, the light guide 962 will appear to an observer to bedark.

In another embodiment shown schematically in FIGS. 10A and 10B, a lightguide indicator system 1000 includes a light absorbing cladding 1002, aporous polymeric film 1004, and a cylindrical light guide 1012. A lightsource 1020 emits light into a surface 1021 of the light guide 1012. Afluid can be present in voids or voids of the porous polymeric film1004. In some embodiments, the light source 1020 can be a LED, such as ablue LED.

When no fluid is present in the porous polymeric film 1004, the porouspolymeric film is mostly air, the light 1030 is totally internallyreflected at the walls 1031 of the lightguide 1012, and remains confinedwithin the light guide 1012. The light 1030 ultimately exits the lightguide 1012 at a surface 1040 at a distal end thereof relative to thelight source 1020. As shown in FIG. 11A, when no fluid is present in theporous polymeric film 1004, the surface 1040 is illuminated and appearsbright to an observer.

Though not shown in FIGS. 10A-10B, the surface 1040 can be diffuse,curved, or non-planar. In some embodiments (not shown in FIGS. 10A-10B),the cylindrical light guide 1012 can optionally be used to direct thelight 1030 to other locations along the light guide 1012. For example,in some embodiments, one or more portions of the cladding 1002 could beremoved so that light exits from the light guide 1012 at specificlocations.

When fluid is present in the porous polymeric film 1004, the refractiveindex of the porous polymeric film changes such that light 1030traversing the light guide 1012 passes through the walls 1031 of thelight guide 1012, enters the porous polymeric film layer 1004, and isabsorbed by the light absorbing cladding layer 1002. The surface 1040distal the light source 1020 thus appears to an observer to be dark.

Referring now to FIG. 12A, in another embodiment an optical system 1100includes a light source 1102 emitting light 1103 into an optical device1104. In some embodiments, which are not intended to be limiting, theoptical device 1104 is a light guide with a rod-like shape or a fiber.Layers 1106, 1108 of a porous material are located along an optical pathof the light 1103 traversing the optical device 1104. Depending on thepresence or absence of fluid therein, the layer 1106, 1108 change fromsubstantially transparent to hazy, which can impede the amount of lightentering or travelling along the optical device 1104. In another exampleembodiment, the layer 1108 can be a porous adhesive that joinscomponents or sub-units of the optical device 1104.

In another embodiment shown in FIG. 12B, an optical device 1150 includesa retroreflector 1152, which is configured to return incoming light 1153to its source. A layer of a porous material 1154 overlies all or aportion of the retroreflector 1152. Depending on the presence or absenceof fluid therein, the porous layer 1154, the appearance of the porouslayer changes from substantially transparent to hazy, which can diffusethe retroreflection provided by the layer 1152. The presence of theporous layer 1152 provides a retroreflector that rapidly detects thepresence or absence of a fluid, and the detection is readily detectableeven at a distance.

Referring now to FIG. 13A, in another embodiment a microfluidic device1180 includes a microfluidic film 1182 with an arrangement ofmicrochannels 1190 thereon. The device 1180 further includes a porouslayer 1184 and a light absorbing seal layer 1186. In the embodimentshown in FIG. 13A, the porous layer 1184 provides a cover that enclosesthe microfluidic channels 1190.

As a fluid progresses within the microfluidic channels 1190, a portionof the fluid enters the voids of the porous polymeric film 1184 andchanges the refractive index thereof, which can in turn change theappearance of the porous layer 1184. As shown in FIG. 13B, the colorchange in the porous polymeric film 1184 forms a wave front 1195 thatprovides to an observer a substantially instantaneous visual indicationof the movement of the fluid within the microchannels 1190.

Based on the composition of the porous layer 1184, in some embodimentsthe visual indication can be designed to change appearance after apre-determined amount of time. In one example, which is not intended tobe limiting, a selectively permeable barrier material can be used thatslows, but does not prevent the ingress or egress of, a fluid.

Embodiments of the present invention will now be further described withreference to the following non-limiting examples.

EXAMPLES Example 1

A strip of a porous polymeric film prepared according to the proceduresin Example 4 below was coated on an Enhanced Specular Reflector (“ESR”)film (available from 3M), and laid flat on a lab bench. The porouspolymeric film included a binder, a plurality of particles, and aplurality of interconnected voids. Then 3 drops of isopropyl alcohol(IPA) were deposited on the surface of the porous polymeric film.

As shown in FIGS. 14A-14F, in the time-lapse process 1300 the porouspolymeric film 1304 was initially bright white in step 14A, and the IPA1303 transformed the film to a silver appearance. Within 30 seconds andwith the aid of lightly blowing on the surface of the film, as shown inin FIG. 14F the IPA evaporated and the film 1304 returned to its initialwhite appearance.

Example 2

Referring to FIGS. 15A-15C, in a time-lapse process 1400, alcohol wasapplied to the surface of a film construction including a seal layer1402 overlying a porous polymeric film 1404. The seal coat layer was anacrylic-based RHOPLEX TR-407 (available from The Dow Chemical Company,Midland, Mich.). The RHOPLEX TR-407 was received at 45% solids, and wasdiluted to 36% solids with deionized water for coating. The targetcoating thickness was 5 microns dry.

Applying IPA as discussed above in Example 1, the color of the porouspolymeric film 1404 did not change for about 15 seconds, then changedcolor at about 45 seconds as shown in FIG. 15A. FIG. 14B shows porouspolymeric film 1404 about 30 seconds after the image of FIG. 15A wascaptured, which was about 75 seconds after applying IPA to the porouspolymeric film 1404. As shown in FIG. 15C, it took about an additionalminute after the image of FIG. 15A was captured for the effect todisappear as the IPA evaporated, which was about 105 seconds afterapplying IPA to the porous polymeric film 1404.

Next, as shown in FIG. 15D, 3 drops of water 1403 were applied to theseal coat surface 1402 overlying the porous polymeric film 1404, whichdid not change its appearance during a time of 5 minutes, after whichthe test was stopped.

Example 3

A small strip of the film of Example 1 was placed inside a disinfectingcap for medical syringes and IV tubing available from 3M under the tradedesignation CUROS. The cap, which was pre-loaded with alcohol, was leftopen to the atmosphere for 30 minutes so as to allow the alcohol toevaporate. When inserted into the cap, the strip appeared to white.

Next, two drops of IPA were dropped into the cap and the film instantlychanged from white to silver. After about 45 seconds, the film returnedto its original white appearance.

The results of this example show that the porous optical films of thepresent disclosure can be used to provide a visual indication of thepresence of alcohol in the cap, which can provide medical personnelinformation about whether the caps retain disinfectant, whether theneedle or IV port covered by the caps are sterile, or whether the capneeds to be replaced.

Example 4

A low-haze coating solution “C” was made, which included the componentsshown in Table 1 below. First, 309 grains of NALCO 2327 (available fromNalco Chemical Company, Naperville, Ill.) (40% wt. solids) and 300grains of 1-methoxy-2-propanol were mixed together under rapid stirringin a 2-liter three-neck flask that was equipped with a condenser and athermometer.

Next, 9.5 grams of SILQUEST A-174 and 19.0 grams of SILQUEST A-1230silica particles (available from Momentive Performance MaterialsCompany, Waterford, N.Y.) were added, and the resulting mixture wasstirred for 10 minutes. The mixture was heated at 80° C. for 1 hourusing a heating mantle.

Next, an additional 400 grams of 1-methoxy-2-propanol was added. Themixture was kept at 80° C. for 16 hours.

The resulting solution was allowed to cool down to room temperature.Next, most of the water and 1-methoxy-2-propanol solvents (about 700grams) were removed using a rotary evaporator under a 60 water-bath. Theresulting solution was 48.7 wt % A174/A1230 modified 20 nm silica, cleardispersed in 1-methoxy-2-propanol.

Next, 63.4 grams of this solution, 20.5 grains of SR 444 (available fromSartomer Americas, Exton, Pa.), 1.32 grams of the photoinitiatorIRGACURE 184 (available from Ciba Specialty Chemicals Inc., Basel,Switzerland), and 87.1 grams of isopropyl alcohol were mixed together bystirring to form the homogenous coating solution “C.”

A coating procedure “F” was developed. First, a coating solution wassyringe-pumped at a rate of 2.7 cubic centimeters per minute (cc/min)into a 20.3 cm (8-inch) wide slot-type coating die. The slot coating dieuniformly distributed a 20.3 cm wide coating onto a substrate moving at5 feet/minute (152 cm/min).

Next, the coating was polymerized by passing the coated substratethrough a UV-LED cure chamber that included a quartz window to allowpassage of UV radiation. The UV-LED bank included a rectangular array of352 UV-LEDs, 16 down-web by 22 cross-web (approximately covering a 20.3cm×20.3 cm area). The UV-LEDs were placed on two water-cooled heatsinks. The LEDs (available from Cree, Inc., Durham, N.C.) operated at anominal wavelength of 395 nm, and were run at 45 volts at 10 amps,resulting in a UV-A dose of 0.108 joules per square cm. The UV-LED arraywas powered and fan-cooled by a TENMA 72-6910 (42V/1 OA) power supply(available from Tenma, Springboro, Ohio). The UV-LEDs were positionedabove the cure chamber quartz window at a distance of approximately 2.54cm from the substrate. The UV-LED cure chamber was supplied with a flowof nitrogen at a flow rate of 46.7 liters/minute (100 cubic feet perhour) resulting in an oxygen concentration of approximately 150 ppm inthe cure chamber.

After being polymerized by the UV-LEDs, the solvent in the cured coatingwas removed by transporting the coating to a drying oven operating at150° F. for 2 minutes at a web speed of 5 feet/minute.

Next, the dried coating was post-cured using a Fusion System Model 1300Pconfigured with an H-bulb (available from Fusion UV Systems,Gaithersburg, Md.). The UV Fusion chamber was supplied with a flow ofnitrogen that resulted in an oxygen concentration of approximately 50ppm in the chamber.

This solution was then coated according to Example “F,” as describedherein, on a 2 thousandth of an inch (mil) (0.051 mm) thick PETsubstrate, e.g., substrate 370, except that the current to the LEDs was13 Amps, resulting in a UV-A dose of 0.1352 joules per square cm.

The resulting optical film 1500 (FIG. 16) had a total opticaltransmittance of about 74.5%, an optical haze of about 55.4%, an opticalclarity of about 99.7%, and a thickness of about 7 microns.

FIG. 16 is a scanning electron micrograph of a cross-section of a porouspolymeric optical film 1500. Particles were coated and interconnected bythe binder used to make the porous polymeric film 1500. Theinterconnected particles formed a network or a scaffold that weredispersed substantially uniformly throughout the film 1500, and thenetwork includes a plurality of interconnected voids with an averagesize of about 50 nm to about 500 nm, or from about 100 nm to about 300nm.

Table 1 summarizes a high-Haze optical film coating solution, “SolutionH,” which was coated at 30.315% solids in a binary mixture of IPA andDOWANOL PM (available from The Dow Chemical Company, Midland, Mich.)with the formulation targets shown in Table 1.

The solvent fractions were 35% DOWANOL PM and 65% IPA, with theproperties of the two solvents summarized in Table 1. The nanoparticleswere in DOWANOL PM, which is a high boiling solvent. IPA is a relativelypoor solvent that helps with gelling, but also contributes to haze.Other formulation targets were a 60:40 ratio of 75 nm silicananoparticles to resin. The 75 nm nanoparticles were used to enhance themechanical stability of the gelled coatings. The resin was SartomerSR444, a trifunctional acrylate.

Two photo initiators were used in the formulation. The IRGACURE 819absorbs strongly in the 385 nm and 395 nm wavelengths and is used forthe gel-curing step. The IRGACURE 184 does not absorb in the 385-395 nmwavelength and absorbs at smaller wavelengths that are matched well withthe Fusion H bulb that was used for the final cure.

TABLE 1 Formulation of standard optical film solution H High HazeOptical Film Solution H Material Density Solid Solution NALCO 147modified 75 nm silica 2.2000 59.113% 17.976% SR444 1.1670 39.409%11.984% IRGACURE 819 1.1900  0.985%  0.300% IRGACURE 184 1.1050  0.493% 0.150% 1-methoxy 2 propanol 0.9190 — 24.320% IPA 0.7854 — 45.271% Total—   100%   100%

Various examples have been described. These and other examples arewithin the scope of the following claims.

1.-134. (canceled)
 135. A fluid sensor comprising a porous layer with anetwork of a plurality of interconnected voids, wherein the porous layeris optically diffusive to at least one wavelength of light when thenetwork of interconnected voids is substantially free of fluid, andwherein the porous layer of the optical element undergoes a detectableoptical change upon fluid ingress into the network or egress from thenetwork of interconnected voids.
 136. The fluid sensor of claim 135,wherein at least some of the voids in the porous layer compriseparticles therein.
 137. The fluid sensor of claim 135, wherein a firstlocal volume fraction of the plurality of interconnected voids proximatea first major surface of the porous layer is greater than a second localvolume fraction of the plurality of interconnected voids proximate anopposed second major surface of the porous layer, and wherein the porouslayer has a thickness of greater than 2 microns.
 138. The fluid sensorof claim 135, further comprising: a first polymeric film is on a firstmajor surface of the porous layer.
 139. The fluid sensor of claim 138,wherein the first polymeric film comprises a downconverting material oran interference reflector.
 140. The fluid sensor of claim 138, whereinthe porous layer is on a surface of a lightguide.
 141. The fluid sensorof claim 135, wherein the porous layer is on a substrate, and whereinthe substrate comprises an arrangement of fluid channels.
 142. The fluidsensor of claim 135, further comprising an evaporative pathway connectedto the fluid sensor.
 143. The fluid sensor of claim 142, wherein theevaporative pathway comprises a vent.
 144. The fluid sensor of claim135, comprising at least one of a pattern, a symbol, a message, a color,a wavelength, or a machine readable code that becomes visible ordetectable when a predetermined amount of the fluid is present in thenetwork.
 145. The fluid sensor of claim 135, wherein at least some ofthe voids in the layer of the porous layer comprise particles therein.146. The fluid sensor of claim 135, wherein a first local volumefraction of the plurality of interconnected voids proximate a firstmajor surface of the porous layer is greater than a second local volumefraction of the plurality of interconnected voids proximate an opposedsecond major surface of the porous layer.
 147. The fluid sensor of claim135, comprising closure device comprising a body overlain by the fluidsensor forming a fluid chamber.
 148. A closure device, comprising: abody comprising an interior chamber; a fluid in the interior chamber; acomponent in the interior chamber of the body, wherein the componentcomprises a fluid sensor, the fluid sensor comprising a layer of aporous material; wherein the fluid sensor undergoes a detectable opticalchange based on the presence of fluid in the interior chamber of theclosure device.
 149. The closure member of claim 148, wherein at least aportion of the body is transmissive to at least one wavelength of light.150. The closure member of claim 148, wherein the component is a fluidreservoir.
 151. The closure member of claim 148, wherein the layer ofthe porous material comprises a porous polymeric film, and wherein afirst local volume fraction of the plurality of interconnected voidsproximate a first major surface of the porous polymeric film is greaterthan a second local volume fraction of the plurality of interconnectedvoids proximate an opposed second major surface of the polymeric film,and wherein the polymeric film comprises a single layer with a thicknessof greater than 2 microns.
 152. The closure member of claim 151, whereinthe fluid sensor comprises a first polymeric film on a first majorsurface of a porous polymeric film, and a second polymeric film,different from the first polymeric film, is on a second major surface ofthe porous polymeric film, and wherein the first polymeric film istransmissive to visible light and the second polymeric film comprises atleast one of a pigment, a dye, an indicia, and combinations thereof.153. The closure member of claim 152, wherein the first polymeric filmcomprises at least one of a pigment, a dye, and combinations thereof.154. The closure member of claim 148, wherein the fluid comprises anantimicrobial liquid chosen from isopropyl alcohol, ethyl alcohol,chlorhexidine gluconate (CHG), chloroxylenol (PCMX), polyhexamethylenebiguanide (PHMB), bisbiguanides, polymeric biguanides, povidone iodine,hydrogen peroxide, octenidine, benzalkonium chloride, alexidinedihydrochloride, cetyl pyridinium chloride, antimicrobially effectivesalts thereof, and mixtures and combinations thereof.